That's not quite the whole picture. Several industrial compilers for languages used by people for work are made by people who recognize that tooling is importan

That's not quite the whole picture. Several industrial compilers for languages used by people for work are made by people who recognize that tooling is important. So the compiler is also a service or set of services with (depending on how you think about it) a database of information to query. It significantly increases the scope of the compiler and adds another dimension of performance and reliability to the system. For example, it may be a good idea to allocate a bunch of memory up front as a part of batch compilation to process some stuff. In a tooling scenario that can be a bad idea unless that large allocation routine is done in a way that the memory is pooled for the many, many requests it's going to get over its lifetime.