Fox's platform camping is basically effective because of his option pool in that position relative to most characters' answers to it.
The main thing here is that Fox has useful SH, DJ, and FJ heights in addition to a solid waveland, powerful aerials, the shine, versatile actions out of shield, fast actions out of shield, a fast dash for clearing the platform, retains huge momentum for clearing platforms with dash jumps, and his back air. Not many characters can really contest directly with that mix. Many characters simply lack a cohesive mix of solid multi-hit aerials, speed, enormous hitbox aerials, flexible projectiles, multiple jumps, lasers, or float that enable them to engage the numerous options that a platform camper can engage in. The strategy itself is basically an abuse of Fox's physics being much better than his opponent's. If you want to see something funny, take a stock from your friend's Pichu on BF with Fox to get a 4-3 lead and then lightshield on the top platform. Then wait. It's funny how narrow the game becomes, right?
The mechanics behind the strat are simple; Fox is made mobile by his fast fall, which enables him to use his vertical movement to dodge and remain relatively uncommitted. The fall speed also allows him to hit vulnerable opponents should an opening present itself. Fox's basic goal in this position is usually attrition or to remain safe from an opponent's most dangerous moves; this is especially true if their most dangerous moves are ground attacks (which have limited utility vs platform-centric styles). This is why platform camp is sometimes used vs Doc and ICs (and other characters of their ilk). Because their aerials are pretty mediocre, those characters focus primarily on ground control with their WD movements and quality ground moves. Platform camping plays against this by forcing them to mingle in the air or take long term damage from safer attacks.
However, Fox also dies from one hit and safer attacks usually means bairs and lasers. So I don't find the strategy itself particularly overpowering. At least when I have to engage it with a top tier character, anyway. I don't care about low tiers and their ability to beat something on principle, so I don't really care if Samus can never beat a Sheik that abuses this strategy or whatever. Or if Pichu really can't beat a Fox who's mastered the technique and Fox to a certain degree.
Platforms basically give zones where Fox can wait in the air indefinitely before dropping through, running off, or jumping off with an aerial. Think of it as similar to imitating Peach's float, except there are some tweaks.
Beyond that, for this character they're largely an added layer of evasion or repositioning (defensively speaking). They add spots to trap your opponent when they're coming down from a bunch of launchers, and they even create some interesting tech trap opportunities during combos. They interrupt his FJ aerial approach and do certain timing things to his jump ins. I could go on. In fact, I could literally go on forever with a topic like that though so not gonna say much else about it. Platforms add depth, that's basically it.
