That's not true, but I'll argue that the real reason is that people who don't care aren't going to be reading it anyway. You aren't forcing anyone to read credits by making them unskippable, you're just making it a hassle for people who don't care, so they'll probably do something else while waiting for it to just finish up. You have annoyed a fan and gained nothing from it. Big win!
I love credit sequences. Not only do I like appreciating the people who made a good game when I'm done, but if the ending was really good, it's also nice to have a break of sorts with nice credits music to reflect on the game before going online and talking about the experience. But hey, if someone else doesn't care for that, they shouldn't have to waste their time with it for no reason.