I don't see that at all. Lawyers in general dress better than most other professions except finance. I've worked in hospitals and never saw the doctors dressing as well as lawyers[1] - some consultants do, but far from the majority doctors. Friends of mine are in architecture, and I don't see that there either. Same with engineering in general - neat casual seems much more par for the course. Academics also don't often fit the bill.

In contrast, the 'neckbeard and star wars t-shirt' is something I've never personally seen working in tech. Neckbeard, yes. I've worked in one waterfall shop and four agile shops, and liaised with techies in enterprise from time to time (zero t-shirts there) - the 'sci-fi geek visible at 100 yards' is a trope, a stereotype. The techies I've worked with have been overwhelmingly male (only one female developer in all that time) and about half of them were family men. That's something the 'computer professional' stereotype actively opposes, instead painting people that are into computers as social losers who can't get a girl.

IT is more accepting of shabbiness in dress than other professions, but I simply don't see the sloganed t-shirt as being the actual standard attire of computer professionals. Instead it seems more to be a shorthand stereotype, just like a white coat and stethoscope signals 'doctor' in the collective mind.

[1] I do have bias here - when I say 'lawyers', I mean ones in business. I haven't had interaction with lawyers dealing in personal matters. I imagine they dress to suit.