That’s what design and art studios do as well. Take contracts to provide something. Dealing with external parties like this is quite different to having employees performing the same job.

This is also quite a common way to bootstrap a small gamedev studio.

Small specialized software product development houses, where there is deep inhouse knowledge of a domain, design and marketing, surely exist.

But these places also like eating, and so will not always be able to work just on projects that fit that mold. Often they need to do unglamorous work such as just being an outsourced entity for a bigger one.

This kind of work rarely gets bragged about on their landing pages.