Context:
Permissive licenses (commonly referred to as "cuck licenses") like the MIT license allow others to modify your software and release it under an unfree license. Copyleft licenses (like the Gnu General Public License) mandate that all derivative works remain free.
Andrew Tanenbaum developed MINIX, a modular operating system kernel. Intel went ahead and used it to build Management Engine, arguably one of the most widespread and invasive pieces of malware in the world, without even as much as telling him. There's nothing Tanenbaum could do, since the MIT license allows this.
Erik Andersen is one of the developers of Busybox, a minimal implementation of that's suited for embedded systems. Many companies tried to steal his code and distribute it with their unfree products, but since it's protected under the GPL, Busybox developers were able to sue them and gain some money in the process.
Interestingly enough, Tanenbaum doesn't seem to mind what intel did. But there are some examples out there of people regretting releasing their work under a permissive license.
If you are the author of the code you want to merge, you can double-license it you know. Hand them a GPL license, they'll be able to use your copy under the same terms, while you and everyone else use your current license.
GPL has no requirements for author attribution which is contrary to the entire point of an MIT license.
That's why I described it as joining the Borg. You release individualism and freely give it to the collective. That's cool, and I get the ethos behind all that, but I don't want to add any of those constraints to my code. I just don't want credit for my work or the others to get lost. I don't think it's a hard ask.
Regardless, we ended up ultimately being a full replacement for the other project.
There is nothing stopping a GPL project using MIT-licensed code except for lack of desire to do the work. They are one-way compatible.
I've actually noticed more GPL-licensed projects give attribution to not only the original author but all contributors.
Whereas I can't tell you how many times I've worked on proprietary software where the company didn't give attribution for MIT-licensed code. Unlike GPL'd code, the author has no way of knowing that they weren't attributed since the code is proprietary.
I believe GPL does have an attribution requirement btw:
There is no section 15 or 16 in GPLv3, but I did find section 7 saying:
But that's an optional thing that you must add onto the GPLv3 license. I'll have to keep that in mind for the future.
That would explain why what I've read mentioned it's not guaranteed in GPLv3 (when comparing to MIT). I'll have to figure out what that notice would look like.