Dude the only time my cat gets anxious is when I leave the house for more than 13 seconds. I'm not saying there aren't cats who are miserable indoors but are you gonna seriously act like all cats want exactly the same thing? They have distinct personalities and some are quite content to be in a quiet, safe space with toys and food and loves and a view of all the pretty birds they they can pretend to kill with their toy. Some cats barely even care about killing or exploring. It's almost like they're individuals.