>>714842106They just needed a counterpart for Knuckles. Originally SA2 was only gonna have Sonic, Knuckles and Eggman as playable characters. When word got out people were pissed Tails wasn't playable so they pivoted to the hero/dark story thing. This is why Tails spends the whole game in a gay mech.
According to Knuckles' character sheet his weakness is girls (he's a shy guy) so making his rival a fat tiddy slut makes perfect sense actually.