My bet is that facing insolvency and the lukewarm reaction to their IPO filings they've reigned in ad spend and are relying on their existing customers to bring in revenue, rather than buying fresh eyeballs.

If that works in the short term, it could make their growth numbers look terrible but make them closer to breaking even (if not outright profitable), possibly delaying the need to bring in fresh capital or at least making their business look like it's worth something, if not $20B.

Continuing to buy boatloads of traffic probably isn't sustainable and while it's possible they could stop buying ads altogether and have a few profitable quarters riding the wave of customers they bought over the last few years, that's not sustainable either.