Because cloud is the new "No one gets fired for using IBM". If you are using dedicated servers somewhere, you cannot have the same reputation of say Using AWS for cloud. Everyone knows the AWSs, Google Cloud etc and no one gets fired for selecting/using them.

I personally have run Dedicated Servers for our business in the earlier days but as we expanded and scaled, it became a lot easier to go with the Cloud providers to provision various services quickly even though the costs went up.