Multi tenancy is expensive. You’d need to have every single service you depend on, including 3rd party services, on multi tenancy. In many cases such as the main DB, you need dedicated resources. You’re most likely to also going to need expensive enterprise SLAs.
Servers are easy. I’m sure most companies already have servers that can be spun up. Things related to data are not.
You wrote "You’d need to have every single service you depend on, including 3rd party services, on multi tenancy.". This is highly incorrect. I worked at several companies that have a multi tenancy strategy. It is:
* Automated.
* Scoped to business critical services. Typically not including many of the 3rd party services.
* Uses data replication, which is a feature in any modern cloud.
* Load balancing, by DNS basically for free or a real LB somewhere on the edge.
If you fail at this you probably fail at disaster recovery too or any good practice on how to run things in the cloud. Most likely because of very poor architecture.
Servers are easy. I’m sure most companies already have servers that can be spun up. Things related to data are not.