In some sense I'm starting to think it has more to do with accounting. Hardware, datacenters and software licenses (unless it's a subscription, which is probably is these days) are capital expenses, cloud is an operation expense. Management in a lot of companies hates capital expenditures, presumable because it forces long term thinking, i.e. three to five years for server hardware. Better to go the cloud route and have "room for manoeuvrability". I worked for a company that would hire consultants, because "you can fire those at two weeks notice, with no severance". Sure, but they've been here for five years now, at twice the cost of actual staff. Companies like that also loves the cloud.

Whether or not cloud is viable for a company is very individual. It's very hard to pin point a size or a use case that will always make cloud the "correct" choice.

Another point (but my common observation) is the responsibility. By going SaaS or using cloud - any kind of data protection, rules/responsibility etc is moved away. and in many ways it is better - Google, dropbox or Onedrive will have better PR to take the pain if something goes crazy. Tickbox compliance is easy.

Something I know nothing about is whether the depreciation on server hardware outpaces the value it creates for a business, creating a tax incentive to own your own metal.