You can login with Gmail or Facebook I believe. Then those rules apply. Why do they force us? Because they want to. It's not only that you worry about your account being hacked, but they might worry about your account being hacked. For you - 1 point SE starter - not really an issue. For SE - in your case - if you don't become an active user - not a problem.
So you start here, you find good answers and support, you enjoy it, you start to become an active and good user, with a weak password. Then you have credibility, and your account gets hacked, spam is posted. I don't know what happens then, but maybe your account is closed or deleted. It's a lot of hassle, SE needs to check your identity - wasted time and energy!
Aside from the fact that all your points are lost, good points you can use to ask attention for problems that got lost, SE loses a bit of credibility. Then they have two other incentives to force us to use good passwords. First it makes it less attractive to crackers to try to break into accounts, and the more difficult it is, the less people will try to do so. The second is one of marketing and education: they teach us, the tech people who should do this anyway, to use good passwords and to find solutions so we can remember them.