Each company have different motivations. For e.g. Basecamp moved to save cost.<p>Working in Enterprise, I can share hybrid model works best for multinational. If they are going into new geography, where local laws restrict data transfer across national boundaries, having a cloud provider with local data centers is the easiest and quickest way to launch.
I opened a PR adding Automattic to the list. They run WordPress.com and Tumblr and all their infrastructure is in 30 private datacenters across 6 continents.
Mentioning Digital Ocean and Cloudflare as on-prem companies makes as much sense as listing AWS and Google. Digital Ocean is one of the world's top ten largest cloud providers and Cloudflare is one of the world's largest CDNs.