It's probably a single dev that made the decision, then moves onto something else. They (probably?) don't have the ability to just raise a recurring PO etc to easily pay you and don't care enough to worth through the paperwork.
If you had a paid licencing model they may have done it, or just found another lib/ wrote their own.
Make your MIT-licensed library big enough that the corpos use it, then switch it to AGPL just before you add a really important and tricky feature they've been waiting for.
I really like the GPL license for that reason. Take it, use it, be merry. But don't you dare use it in a closed source project, and you have to give me credit
Just use a GPL license instead. It allows use with credit, but requires that usage also be released for free. Meaning that it can’t be used by corpos and their closed-source projects.