Dropbox is in a relatively specific situation wherein their cloud costs would be extremely high (storage, bandwidth) and their in-house technical skills are probably quite good.
Second point is spot on. Not many companies have the engineering capabilities. Dropbox has so much potential, but their business vision wasn't great to say the least.
Dropbox is itself a cloud provider. A consumer/SMB cloud provider. It makes total sense they build up their own infrastructure, not only from a purely profit/scale point of view.
It's about their core values and identity, at least because in this way they are seen in the market as a big player and not just as another AWS reseller with some added benefits.
There's a lot of companies that have the scale to benefit from running their own tech, fewer who have the skills and number of people, but it's not a small niche even so.
Netflix is a counterpoint? A good fraction (though not majority probably) of their cost is probably bandwidth and computation yet they continue to offload that to a cloud provider, who's a direct competitor no less.
netflix does not serve their bits over amazon. they have their own major infra, and operate a large and distributed cdn, including edge caches colocated within eyeball networks.
it would be insane for them to deliver their video content over aws.
Netflix does run their own CDN for video content, presumably to avoid that exact problem. I would imagine that's by far the most expensive part of their business.
