For my wife, because it ruins her lipstick less than a lid with a hole in it.
I've heard some people say they do it because they think it reduces the effect of the soda/coffee/whatever staining their teeth.
I think it just increases consumption because you don't feel it filling your mouth as much as when you drink from the rim of a cup.
The ethics of straws just won't move the needle.
I mean this only mostly in jest. Iced coffee drinks really are to me a particular indicator of overconsumption.
If you have a compromised immune system, straws are important part of staying healthy.
If someone is immuno compromised I think this makes sense to extent.
In such an environment, sipping from a straw tends to work significantly better than drinking from the rim of a tilted, open-topped cup.
While smaller drinks might use a lid with a small gap in it, that just isn't a practical option for larger drinks.
(edited to remove claim that straw is no better than secure lid with a small hole, it could be a little better)
(I don't mean this reply to be a defense of the market either. I'm asking you to evaluate what is core to your criticism)
Except for Ad industry and marketing.
And in the context of this discussion, you might be asked to prove that straws are used purely because of the manipulations of marketers.
I work in a business that serves a lot of local advertisers. We do take national and agency client business, but the majority of our work is with local businesses. They do it because it works. People hear the ad and foot and digital traffic to their locations increases.
Advertising is just a market. "Advertisers" are just people with a business who want to reach consumers. I'd be far more comfortable with the case that, as a market, it should be policed by some administrative agency, and like most administrative agencies over the past few decades they're likely asleep at the switch and so the market shows obvious signs of abuse.
This is why I, and the other poster, take some umbrage to what seems to be a very simplistic elitist take from you. This is a market. It has benefits, and it has the potential for abuse. Rather than looking at this as a social problem that simply needs basic agency actions to be solved to defend those benefits, the rather radical idealism of destroying the market entirely gets bandied about a little too comfortably.
My problem is with poor education and critical thinking skills, and the anti-intellectualism on display whenever you see full-grown humans stamping with their fingers in their ears because “I just want what I want!”