It's similar to the issues with microservices. You've broken something that could be "simple" single monolithic application into many pieces and now there is huge complexity in how they are all joined together, fragemented state, latency, transactional integrity, data models, error handling, etc etc. Then your developers can't debug or test them properly, what used to be a simple breakpoint in the debugger and stepping into a function call and directly observing state requires a huge complexity to trace what is happening.

All these things got much harder than they used to be, and you're living with that forever - to pay for a one-time saving on setting up some self-updating, auto-scaling infrastructure.