Actually, I was only meaning use it internally to improve their own workflow.

They can still bundle it with other things, only release your code, secretly improving only what they did on top of your API and make money out of the bundle, so why stoppping there and using a free license rather than something with a NC clause?

On the other hand, one could argue that GPL would refrain a corp from including your software in their product, while at least the cite you get with the MIT license at least gets you some advertisement and potential contirbutors.

What if other free software developers use a license incompatible with the GPL for their own reason, is it OK to deprive them from the right to simply incorporate your code in the name of fighting big tech?

I don’t mean to say that it does not make sense to use the GPL, it is probably the most sensible choice if your aim is to fight big tech corporations. But not every piece of software is written as a commercial weapon.