On the other hand, there are players like me who will gladly learn more characters for the fun of it. And especially if we're given chances to show off our lower-tier skills without threat of higher tiers, people like that would be even more inclined to compete.
Your post and the post you're replying to has a major difference though: You make the choice to play multiple characters.
Why
force someone to play the game the way you want to play it? If you want to use and rely on multiple characters (I know someone like this at my scene), then do so. But if someone wants to play just one character and fully rely on it, then they should also do so as well without being punished for it. Outside of all of the logical arguments that has been made against this idea, this is something that really should not be ignored.
Furthermore, this has been really bothering me so I'm going to be really frank: Your posts gives me the perspective that you view yourself as a special snowflake. That for some reason, no one plays more than one character for fun. I'll show you that this is not the case.
I can make a full list of the characters I've played for fun and picked up as secondaries, and I can tell you it's more than five (and one of them is Samus, a character I enjoy nearly as much as Mario but she is one of the worst characters in this game). So if you do stuff like character strikes or character DSR, I'm not SoL, but if I want to play Mario then I will play Mario whether you like it or not and no one is going to tell me otherwise.
Nairo plays Pit, Dark Pit, Robin, ZSS, and Zelda. He views himself as a Robin main.
Ally plays Mario, Shulk, and Diddy. He's a Mario main and he enjoys Shulk but has stated that Shulk is bad against Diddy.
ZeRo has stated for the record that he has played at least 400+ matches with
every character in the game.
Nyani plays Mario and Pit.
Espy plays Sonic and Little Mac, and prefers Little Mac against Diddy.
I can list even more but my point is made. Multiple players play multiple characters, but the majority of them will prefer to stake their tournament life on one character with few exceptions, because as multiple people have stated, players tend to gravitate towards one character that they will favor and truly invest in and make it their best character.