I feel it's fair that they're on AWS right now. Generally the arc of MVP->IPO involves using the cloud to find product market fit, and as that fit improves your revenues should also. Moving from the cloud to a colo would then be driven by capital investment to bring down COGs; to either improve PPS or get to cash-flow positive.

Heap using AWS just means they've not yet reached a point on that trajectory where the capital investment moves the needle enough to warrant it. That could be for any number of reasons.