Some companies do require it. Essex Property Trust is one that does. It's a smart move really. National average cost is like $13 a month and it protects a considerable amount. In fact, we have our insurance through American Family on our cars and we practically get our renters insurance free, which covers up to a half a million dollars in losses. I actually am very partial to them. My agent is really awesome and easy to work with!
The big benefits for your residents are that when their dishwasher overflows due to their negligence and floods the apartment below them and ruins a bunch of stuff, they aren't paying to replace their neighbor's stuff out of pocket. Also, it's nice to buy piece of mind at a low cost.
And it is so common place with many communities in the Seattle area that renters don't give you as many funny looks about requiring it as you might think. They tend to already have it for the most part and when you tell them it's less than a Netflix subscription through different companies, that's pretty easy to stomach.
A lot of communities work with an insurance company for referrals, as it can be a great source of ancillary income. Just make sure you pick a good company. If you're looking for something portfolio wide, I suggest making sure that the company you want will cover you in all states. American Family, for example, doesn't work in California, but they are here in Washington. If it's just for a regional portfolio, or even just for your property alone, then go with whomever gives you the best bid
Good Luck!