Meshes are there to abstract away stuff that is much more manageable in a monolith. If you have 100 microservices implemented using 5 different platforms you need libraries and programming discipline to implement retries with backoffs, circuit breakers, health checks, tracing, service discovery and other similar stuff in every single one of them.

In a monolith you need to implement some of this stuff only once and you don't need a lot of it at all because you are not making remote procedure calls.