Definitely the easiest insurance line to get started in for a variety of reasons. Things like easier compliance, younger and uninsured demographics that are easier to market to, and reduced complexity
Regulators also don't put as much financial scrutiny in lines that don't have high caps (although they still scrutinize other aspects like consumer protection).
If a "renters only" insurance agency goes under, most guaranteed funds could pay it out without much consequence. It is a whole different story if a major health insurance company were to go under.
I understand how their model is a bit different from other insurance companies, and I think that's cool. But I'm still left wondering why they thought this form of insurance (as opposed to auto, life, etc) was the easiest to attack.