Reinventing that basic logic takes a lot of code and time for a bug-ridden, worse, half-implementation. And on top it will be completely home-grown, any new hire will have to learn it from the barely existing internal "documentation" that wasn't touched in years - making not only initial development multiple times more costly, but every subsequent maintainance as well.
Meanwhile I can just add 3 annotations in Spring/RoR/Django and have solved the problem in a way that a competent new hire will instantly be familiar with.
Also, even the supposed benefits are questionable at best - mechanical sympathy? Like, most of these frameworks sit on top of a highly efficient C web server that just calls some business code for nanoseconds and that's all the "overhead". Python and ruby backends are all over the web and they perform completely fine, even though these are interpreted languages. Java/c# won't even have that problem. I have seen plenty terribly performaning home-grown solution which were designed by a "smart" software astronaut - it's almost like writing a proper web server is a different skill set than typical CRUD business apps.
And lastly, Go feels more productive because it is chock-full of boilerplate. So you can type and type and feel you are so productive, meanwhile in another language you would have just added an annotation and 2 lines and called it a day - it's just a psychological "trick". And "libraries that are easy to compose"? Like, which language has an ecosystem with libraries that are hard to compose? What tools do Go have that would aid in that? I would argue that a more expressive language have way better tools to help with code composition, wouldn't it?