If your monolith goes unwieldy you have a problem with your code structure which microservices won't solve. As we all know, you need well isolated, modular code with well defined boundaries. You can achieve this just as well in a monolith (and you can also achieve totally spaghetti code between microservices).
Microservices is a deployment choice. It's the choice to talk between the isolated parts with RPC's instead of local function calls.
So are there no reasons to have multiple services? No there are reasons, but since it's about deployments, the reasons are related to deployment factors. E.g. if you have a subsystem that needs to run in a different environment, or a subsystem that has different performance/scalability requirements etc.
Microservices is a deployment choice. It's the choice to talk between the isolated parts with RPC's instead of local function calls.
So are there no reasons to have multiple services? No there are reasons, but since it's about deployments, the reasons are related to deployment factors. E.g. if you have a subsystem that needs to run in a different environment, or a subsystem that has different performance/scalability requirements etc.