I don't think it's true that the only alternative is loan sharks. It's mostly "traditional" payday lenders, many of which are owned by the big banks (through a couple layers of obfuscation to cover up the stench).
That said, the "traditional" payday lenders all turn out to be quite predatory, don't they? (I understand that's what the original founding premise of LendUp was intended to address, even if they couldn't make it work.)
But aside from that, will the traditional payday lenders lend to everyone and anyone, no matter their circumstances? If not, what are the options for people who they won't deal with?
There of course is another possibility: the founding team in 2011 was proposing a concept that seemed ethical and an improvement over payday lending options that existed at the time, but over time the company's idea or execution changed for some reason, in which case, there was neither poor ethics nor poor judgement on YC's part.
Occam's razor would require us to accept this explanation unless there was substantive evidence for another scenario.