Because dressing nice makes your vibes better and people treat you better and are more willing to accommodate your requests.
This is probably the part of the case for dressing nicely I find compelling, but to be fair it’s a big one. Beyond this and signalling, what other reasons are there that people wear nice/expensive clothes?
Anecdotally, the one time I wore a blazer for a flight (because I heard that you’re more likely to be bumped to business class), a stranger asked me if I’d like to be their free plus one for their airlines’ lounge. Relatedly, I’ll be flying for the first time since getting my PhD in a few months. I’ve heard that doctors get treated better by airlines (maybe because they assume they are all medical doctors and would be useful in an emergency?). I see my ‘Dr’ title in a similar lens as nice clothes. I don’t really care much about it, but it can be useful and help me achieve my goals, so I should probably get over my mild discomfort with seeming a bit ‘wanky’ by using my title. I’ve already noticed that people think you’re smarter about things unrelated to your research just because you’re doing a PhD.
Shouldn’t it be: ‘They pay you $1,000 now, and in 3 years, you pay them back plus $3,000’ (as per Bryan Caplan’s discussion in the latest 80k podcast episode)? The money won’t do anyone much good if they receive in it a FOOM scenario.