It makes all the sense in the world, they are companies, they like money, they don't even "sell" you their games, they only give you a license to use them.
If you have one console in your living room yes, all people can login, buy games and play them. If you own two consoles it depends, if both are yours no problem, you can use both, if one is for your little brother in theory no, you cannot let him use your account, he has to create his own. Enforcing that is a terrible hassle not worth it, so they won't do anything, but if your little brother goes to college and takes the console and keeps playing the games with your account, these companies are completely free to ban it based on those grounds, in that case is more enforceable, since they can see the login times and ips of both consoles as being in very different locations. They won't do it because it is still a hassle, but they are perfectly free to do it, you clearly didn't read that small print.