Never mind that you're most likely sitting in an office alone or with co-workers all day. Why would you dress up like a lawyer when you have no contact with clients? Getting a dozen suits is quite expensive, never mind the laundry costs. It just strikes most engineers as quite ineffective.
"It's not for others, it's for your own self-esteem!" Really? That sounds a lot like the argument a car salesman would make. So me riding around on a bike is a bit childish, too? Yes, suits, cars, toupees, escorts – all might help a few people, but aren't we fighting symptoms instead of root causes here?
I'm in my thirties now, and I understand the pressure/urge of "dressing like a grown up". I do have some saddle-stitched shoes, English shirts and a few suits (most of it a bit too big, as I've lost a few pounds recently). I'm aware that "woot" shirts don't flatter anyone's physique…
But trying to fit in by dressing a certain way isn't exactly the epitome of growing up (one might argue about that). So dress up nice if you think that particular style makes you look better (and there is a certain evolution of mens wear…).
I just disagree that you a) have to, and b) about what to wear. In my opinion chinos + dress shirts are hardly better than t-shirts and jeans, so that seems hardly worth it. And well-tailored suits are quite high maintenance in comparison and difficult to choose.
TL;DR - That's why I'm wearing my Star Fleet uniform all the time.