[gaius]

It seems like the training and cost of always needing to build your own frameworks would be exceptionally high

It is purely a matter of volume - are you doing enough business to make it worthwhile?

The last company I worked for had in-house database, programming language, IDE for that language, version control system, job scheduler... At the time they started doing that there was nothing available that did what they needed, and even now, their stack does things that I'm not sure I've seen outside, tho' 10 years on it's less clear that it would be worth starting a project like that from scratch now.

Remember, in business, there are no concepts of "cheap" or "expensive", there is only "worth it" or "not".