Well, there's still people who like to site and just enjoy the concert and the music, and I don't think artists consider that rude. They came to the show after all. :p Also people who aren't able to stand for 3 hours, with disabilities but without wheelchairs, people who don't like crowds, also children sometimes, older people, sick people... The crowd is not for everyone either.

I actually sometimes find it sad that the smaller venues don't have some seats for these people.