Of course, I said proprietary. You said commercial.
Proprietary refers to ownership and licensing. While I somewhat conflated it with closed-source in my comment, it nevertheless applies since we are talking about the ability to make it closed source.
You can relicense derivative works of MIT or BSD software provided that you satisfy the original license requirements (attribution). This is irrelevant of commercializing it.
Conversely, and to your point, you can sell GPL software you didn’t write, or sell a derivative work of it, but because of the copyleft nature, your derivative work must also be licensed under a compatible GPL license.
Proprietary refers to ownership and licensing. While I somewhat conflated it with closed-source in my comment, it nevertheless applies since we are talking about the ability to make it closed source.
You can relicense derivative works of MIT or BSD software provided that you satisfy the original license requirements (attribution). This is irrelevant of commercializing it.
Conversely, and to your point, you can sell GPL software you didn’t write, or sell a derivative work of it, but because of the copyleft nature, your derivative work must also be licensed under a compatible GPL license.