For startup phase, its all about speed, I can provision new machines, databases in minutes which have sane defaults and predictable behavior. I do not have to worry about configuration, backups etc. And, its not about difficulty, its about speed, if I have to recruit one less person (which is ungodly difficult tasks), or spend more time on product, I'll go for cloud.

For large companies its again about flexibility, while they can manage/own data center. Core products with predictable load are good for data center. But in SOA or microservices, where a team is responsible end to end for service, cloud is godsend. Getting a new bare metal server is slow and bureaucratic. Boxes are assigned to cost center and getting them moving around is difficult. Getting temporary servers for an experiment is difficult. So the company has to go for internal cloud or external like AWS