Google have struggled to retain focus. And when they started out, they chose to compete on datacenters as a core competency: their corporate history is full of the idea that they could run a search engine cheaper/better than competitors by using commodity PCs and that kind of thing.

Facebook is a similar story: being the biggest website in the world is a core competency for them, and one of the ways they outcompeted rivals early on was by scaling their website better.

Uber has yet to turn a profit.

If datacenters are a part of your business proposition - not necessarily "we're selling datacenters to other people" but rather "we will be able to outcompete our rivals because our datacenter strategy will be better" - then self-hosting makes sense. But if the datacenter is a commodity from the point of view of your business - and I would assume that would be the case for Lyft - then it makes sense to buy off the shelf.