If you're going to run alternatives to cloud services and call that good enough, then the same is also true for mainframe development.
Meaning, I can't run DynamoDB locally but PostgreSQL is close enough for most tasks, so sure I can kinda run that workload locally, but I won't learn any implementation-specific issues about how it would behave in AWS.
Similarly, I might have a hard time running DB2 for Z/OS, but I can also run it on Windows or Linux, and in this case I'm far closer to the actual development environment. Same is true for most of the dev tools and services commonly found in Z series environments.
I would argue the commenter above you is flat-out wrong: for most core AWS and Azure services, it's far easier to put together a home, single-desktop-PC-based dev environment for mainframe than it would be for cloud if you don't have the ability to actually use the cloud directly.