This is completely ignorant of the fact that landlords can get insurance for those things and often dont have to pay anything at all

They still have to pay insurance to get insurance. And I'm not sure you can get insurance against the roof getting old (not in my area anyway). When the roof is too old and needs replacing, you do it out of pocket/bank loan. Complete roof replacement are not so often (depending on material), so you can (and should) as a home owner save up to this.