because marth is actually an amazing character. his neutral is fantastic because he has amazing spacing tools that make him formidable to approach and hard to pin down in general. nair and fair are both very safe spacing options with a ton of reward, including combos (nair has kill confirms) and potential tech chases/frame traps. nair can be used for crossing up opponents on approach and gaining reward in general out of approaches. back air can also be spaced safely. up air is quite safe and fast - a good option for frame traps and offensive pressure. all of these moves can kill very effectively as well, making marth a scary character to approach and challenge in general. that's not even mentioning his elite ground game, the best move of course being jab which is utterly ridiculous, confirming into combos and kills with ease. forward tilt and down tilt are also excellent pokes and spacing options; forward tilt is particularly good when you pivot it and dtilt is a solid poking tool, even setting up tech chases sometimes. dancing blade is of course a great option as well, a bit unsafe but still very solid/consistent for punishing and mixups. this ground game is made better because marth's movement is amazing with one of the best walks in the game, a solid perfect pivot, and one of the best extended dash dances. there's up b oos to escape pressure, which is also obviously unsafe but a very consistently effective option that prevents marth from being kept in shield. marth can use so many different amazing options in neutral whether utilizing his grounded movement, sh/fh aerials, or simply his ground game. many characters just can't deal with all of these options and get demolished by marth's neutral.
and then there's the fact that marth is so explosive and scary to fight. his aerials all kill at normal ko percents (100/110ish). tipper fsmash practically kills when you spawn and is a relatively quick move to throw out. jab leads into kills, including very consistent options in ftilt and tipper dancing blade, which kills ridiculously early. up tilt kills. if you feel too safe in shield, marth can shieldbreaker and kill you at 30. he has a consistent kill throw in up throw that generally kills ~130/140 and even a dthrow uair kill confirm on certain characters. getting hit can be so scary because marth has the range and proper frame traps to cover landings, really keeping his opponents from landing or simply kill you with the correct option coverage/read, and an elite ledge trap game due to jab and the other options at marth's disposal, including some of the most rewarding options for 2 frame catches in the game. even though he doesn't need it, marth also has really good edgeguarding. if we're talking about rewarding characters and characters that have "x factor" or jank, marth fits in right alongside those characters in addition to having the fantastic neutral.
what are marth's flaws? he can have trouble landing if he can't create a little bit of space to cover himself with an aerial and his opponent doesn't let him get away with the dair. his recovery can be a bit exploitable, though it's far from bad. his disadvantage state in general is a bit underwhelming, though up b and up air as well as certain other situational mixups help a lot. also, marth can definitely juggle you and ledge trap you, but he's not going to do a 50% combo. marth in certain respects definitely has to work for the percent he gets (though leo has shown that the way this was portrayed in the past was heavily overblown), although the percents he can kill you at and jank he possesses are crazy regardless. marth loses a few matchups, probably -1 vs sheik and maybe losing to a couple other characters - bayonetta and zero suit being the main ones that come to mind, with mk also being on the radar. none of those matchups are really bad, but in terms of top tiers we don't really see marth dominating much either, mostly having even matchups aside from mario (a matchup he wins) and potentially 1-2 other slight advantages. his matchups against other characters tend to be very solid overall though.
if we look at results, marth has many players putting in work. though not entirely on its own, leo at least used marth only in top 8 of the last two tier 1 events (genesis 4 and zero saga) to take the win, making marth one of the few characters to win a tier 1 event, let alone multiple. he's also currently the second best player in the world. mr.e, though a notably inconsistent player, has some fantastic wins with marth, such as over zero, nairo, dabuz, and ally, and 1 top 8 at a major (ugc) alongside multiple top 16s and a number of significant regional-level results over the past year. he's probably ~top 25 in the world with solo marth. pugwest has wins over the likes of anti, marss, mr.e, and tweek and a number of top 32 (17th/25th) placements at majors, all with just marth. fuwa is ranked on the highly competitive japanese pr, regularly achieving top 16 and top 8 placements at japanese events with wins over komorikiri, earth, taiheita, hikaru, some, goma, and more. rizeasu, though far from a solo marth, is also ranked on the japanese pr and has notable wins with marth himself, such as taiheita, kuro, hikaru, you3, shogun, and fuwa. false is less active and doesn't only use marth, but his marth has found some significant success in helping him achieve notable wins and success at the majors/regional events he does attend.
marth has the neutral, the ability to maintain advantage state, the explosive capabilities to clutch out matches and turn them around at any times, the reasonable options in disadvantage, the matchups, and the results to back up his placement as a top tier character. in fact i think he may even be a little underrated in his current position, though it's all arguable.
(Possibly
