There is a simple reason you haven't considered.

I want to bring my suit on the trip, and I don't want to crush it into a bag, because it'll wrinkle.

Human bias. People tend to treat you favorably when you dress a bit nicely. You don't have to over-do it, but you also don't want to appear "rough". I've travelled both ways, and can tell you for a fact, you get hassled more if you look like you just rolled out of bed, as opposed to someone who's at least trying to look presentable.

I always put on pants when I go out. It's the decent thing to do

My company was very old school and had a dress code for all stupid situations, including travel on business. Also, fly in and fly out meetings are a thing. In the 90’s they wouldn’t let you sit in first class - before points aligned status were a thing, travel enough and you would get bumped up often when in a suit over others.

I never understood why not. Dressing up "nicely" doesn't need to be uncomfortable at all. If the clothes fit well and are suitable for the occasion and location you can be comfortable and be dressed nicely.

What I never understood is people going out in pjama's or sportwear while acting like those are the only comfy clothes in the world and the rest of the people are making themselves have a worse time. Be it at airports/planes or elsewhere. Putting on decent pants take 2 seconds and can be just as comfy, so time and comfort aren't really much of an excuse. People should invest in good basics for day to day use, you'll earn it back in daily comfort.

But also, some people simply enjoy looking a certain way. Even for less comfortable clothes, that enjoyment can be bigger than the discomfort making it worth it to them. It's not always about having a reason.

Because I come from a family of pilots and the free F&F tickets came with the stipulation that we dressed very nice. I grew up with that and the habit stuck.

They probably dress nicely most of the time.

at the airport you also have higher chances to meet people from different countries and cultures with different standards for what is casual clothing. A fancy dress for an American is an outfit to go at the grocery store for an Italian or a French

Apparently you should at least avoid wearing shorts on planes. There's multiple reasons, including not sticking your skin where others people's skin have been stuck, but the most important to me is because of the slides in case of emergency.

If you wear shorts and for some reason the slides have to be used to exit the plane, you risk being burned.

I think it's because some people like to look nice

I'd say.. why not?

I like clothes. When flying was a bigger deal people would dress up. With the democratisation of air travel, nobody does any more. Still, in my head it's an "excuse" to dress up due to the old etiquette. It feels good to me to arrive at a new place and look put together while I'm at it.

Look good feel good, switch to the PJs in business class...

I wore suits and ties for many years, and now that I'm retired, I'll never wear another tie again.

Most days, I wear loose cotton pants, a t-shirt, and maybe an open shirt over that. And sneakers. Probably not even socks. If they don't like it, Fuck'em, I really don't care.

I'll put on big boy pants and a nice shirt if we're going out for Christmas dinner, and I'll wear socks, but it's still sneakers. And no tie, ever.

Gotta be classy sometimes yk

Poor = bad to most, even subconsciously

One reason among several is tradition. Air travel used to be the domain of the wealthy, at a time when the wealthy seldom left the house in super-casual or working-class attire.

I don’t dress formally, but I always try to put effort into my outfit. Why not look good if I have the choice?

Wearing a shirt and nice trouser helps my business traveller persona dont want to explain an immigration officer why I wear work clothe and steel toe booth for a business meeting.

Anyway, I have a business meeting, need a suit and will be back the next day, so I am rather wearing my business suit, rather than taking a checked in luggage

As utilitarian as pyjamas are, not everyone finds them to be in good taste.

It used to be good manners to dress up for stuff like this, probably left over from that. People would wear their church clothes when traveling.

I actually find office/dress wear extremely comfortable.

Like to the extent I actually will wear more casual clothes to work to make sure I stay awake some days.

Habit. And I've become good at finding outfits that look nice and are just as comfortable as ones that look more casual.

Why don't you wrap yourself in a bag to go shopping? There is no reason to look nice.