You go way back into the 1980's every compiler vendor was trying to drink your milkshake[1] via licensing fees for compilers and libraries.

Two companies that didn't do that were Microsoft, Borland. AT&T was forbidden from selling products outside of Telcom. Which is why Linux and C/C++ succeeded. C succeeded because a competent grad student could port the language to a new computer in a two months.

So you could use Microsofts Basic and C/C++ compilers, Borlands Pascal and C/C++ compilers, or gcc/etc C compilers without the them sharing ownership of your compiled binaries.

[1] Per unit licensing fees. Meaning instead of just charging you a seat license, they wanted a cut of your profit as well. You pay use $20 for every license you sell. I'm not kidding about $20 either.

GPL makes it harder to charge people for spyware. It also makes it possible (at least theoretically) for users to fix bugs themselves, which breaks the bug-fix middleman monopoly that aspiring spyware vendors seek.