Idea
The Pun Tyrant
In Boku no Hero Academia, one thing that is extremely important to understand is that practicality is subordinate to the image you give. It's everywhere in the series, with even the main conflict being between the symbols of peace and evil. For example, All Might's costume has 0 practicality to it, except maybe being baggy enough to not get ripped to shreds when he transforms. But this is a big reason as to why it is effective: it shows that with his own power, the #1 hero can defeat any threat just with the power of his fists and his courage. It inspires and gives peace and courage to the people.Is there even a reason to do impractical costumes like the one I posted earlier? Considering that most of that stuff is cosmetic and not good for hero work in general, but people do seem to lean towards those types pretty often.
Have a tank suit.
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Fighting villains is a very small fraction of a hero's job. Many of them maybe take on one or two villains in their lifetimes, usually simple thugs whose quirks are about as effective as "cardboard cutting blades". The vast majority of heroes don't really need to be practical so long as they are competent as heroes, which already includes passing difficult exams and harsh training, not to mention having actual experience and training in using your quirk, which your average thug just won't have cause it's illegal to use them in public unless you have a hero license AND the law allows you to classify the situation as an emergency.
It is also important to understand Hero costumes, unlike quirks, are not bound to a user. A hero costume can be stolen, and it can interfered with much more easily than a quirk. And if a hero is used to relying on a piece of tech rather than their own power, if they face a situation where that tech is less than stellar it won't just come off as a hero having a hard time because of a bad matchup, but it will make the hero look downright incompetent, since they are just relying on the hero costume or so it may seem.
So in short, a hero costume that is too practical steals protagonism from the hero, can be stolen or rendered useless, may create bad habits for the hero, and may not even be needed given the power level of the average criminal vs that of the average hero.
We could also go into the fact that hero costumes that are mechanical would be hella more expensive than just stylish things and a widespread use of them would take from the indidvidualtiy of heroes, thus making them harder to recognize by the public, and other similar logistic issues.