It is "muu muu" , a loose fitting dress, some of these dresses can be very stylish for certain occasions and if you know where to shop for them and how to accessorize. The same as caftans and sarongs.
Although I am thin, have decent muscle tone for my age and my skin isn't heavily sun damaged, I choose to dress modestly and age appropriate at 60 plus because I rather be viewed as growing old gracefully than delusional.

Also, if you have a nice figure, you can wear slightly form fitting clothing that doesn't reveal a lot of skin but does show off your figure, unlike a muu muu. Lastly, no one wants to see crepe paper cleavage
As for young women, it is 2025 and many young women push the limits, even those who are overweight and should be modest. It is mostly because they are attention seekers. But also, I believe it is partly because our society has been sexualizing young girls more and more over the last 3 decades and part of that can be seen in the styles of clothing available to pre-teen girls.
As for young women bike riding in skimpy tops, if a woman is silly enough to not protect her skin/body while riding a bike, then she may learn the hard way at some point. I've seen those types on the rail trails I ride my bike on and they usually don't wear helmets either. So road rash may be the least of their concerns one day.