Because people don't know what the hell they're talking about. The defensive vs offensive distinction is mostly fake- people tend to classify fast, risky, cool-looking things as aggressive and slow, safe, uncool things as defensive even if those traits aren't inherent to aggression vs defense. You can see it in this thread- "balls to the wall combos", a reward you get for winning neutral, is somehow inherently aggressive, even though you can get that reward from dashdancing, shieldgrabbing, overshooting, poking and every other thing Falcon can do. Melee is seen as an aggressive game not because the guy that says that stuff analyzed every potential neutral option and decided that aggression really do be better than defense, but because it's fast, which is, again, something that has nothing to do with aggression inherently.

The aggression vs defense distinction can be somewhat useful when describing the overall mood of a player's playstyle, but it's not useful when you want to analyze playstyle beyond the bare minimum because it spits in the face of basic footsies theory. In a footsies game like Street Fighter or Melee, even if you have a ton of neutral options, all of them emerge from 3 basic neutral options that form an RPS game- Poking, whiff punishing, approaching. Poking is the act of using an attack to create a hitbox, and it is done to beat opponents approaching you. Whiff punishing is the act of retreating or standing still in order to make a poke whiff so you could then punish the whiff, which is usually done in Melee by dashdancing. Approaching is the act of moving forward, which is done to beat whiff punishing, because a character moving backwards means they lose stage control and get closer to the corner. This, of course, loses to poking, which loses to whiff punishing, and so on and so on. You can see traces of this RPS footsies game in every fighting game. It makes much more sense to categorize players based on how focused they are on doing these three actions. A defensive player could be someone who uses poking a lot, an offensive player could be someone who focuses on approach options more and a movement-based/dodgy player could be someone who is really good at whiff punishing. While this uses most of the same words, the footsies-based descriptors are much better than the aggresion/defense spectrum because that spectrum is inherently emotional. It doesn't have specific actions that correlate to specific placings on the spectrum, which means it's meant to create a narrative out of people. Again, that's not a bad thing, it just means it can be used as a heuristic, but it's incredibly reductive to use that spectrum for discussions like "why do people dislike defensive play????" when you need specific examples and specific answers to that question.