MIT: I build my thing on top of your thing, it’s my thing now. I sell it, you have no rights.
GPL: I build my thing on top of your thing and your license forces me to distribute my thing under the GPL, including the source code.
There are legitimate arguments for both. Sometimes it sucks when proprietary things get built on top of MIT code but sometimes it takes money for innovation, and in the realm of code the world often benefits anyway by virtue of copycats or distillation.
MIT: I build my thing on top of your thing, it’s my thing now. I sell it, you have no rights.
GPL: I build my thing on top of your thing and your license forces me to distribute my thing under the GPL, including the source code.
There are legitimate arguments for both. Sometimes it sucks when proprietary things get built on top of MIT code but sometimes it takes money for innovation, and in the realm of code the world often benefits anyway by virtue of copycats or distillation.