That's largely limited by ticket sales nowadays, right? Responsible / law-abiding venues (in countries with good regulation on it) don't sell so many standing tickets that the risk gets too high

The wiki page you linked in the other reply has a link to a list page https://en.wikipedia.org/wiki/List_of_fatal_crowd_crushes

You'll notice that very few recent ones are at concerts, and those that are consistently involve serious mismanagement of the event and usually something inciting large-scale fear responses

You are right that it's less safe that being seated, and you do need to watch out for your surroundings and be ready to get yourself out if you think it's too much. It is a problem that we know how to handle for the most part without banning all standing areas, though