[gf000]

Most projects won't stay a hello-world REST service, there would be no point of doing them. They will grow and most likely make use of a bunch of CRUD features, on which we have a lots of experience in various languages and frameworks can solve a good chunk of any problem that might come up (AuthN/Z, session management, endpoints, safe parsing from and to json/url/forms, etc).

Spring (besides itself being modular, so you only "pay" for what you use) will solve all of that for me, so I only have to write the small amount of business-relevant code and be on my way. Later on, some other developer who knows spring can join the project and feel ready at home.

Compare it to a buggy, slow to develop, slow to onramp home-grown half-solution, and it's quite a clear tradeoff, unless there are very specific requirements that make the usage of frameworks a no-go.