They might be trying to roll some new stuff out. I don't know about Stripe's financial internals, but they could have stable financials, but a major project in mind and need cash to run for it. VC money's probably way easier to get than a $500 million bank loan for them.

Last I talked to someone at Stripe, my impression is that they were still relatively small in terms of staff (I think someone said 100 in total across the world?).