I wrote a paper on this in grad school. A few of these services (I cannot recall which and I don't have a copy of the paper handy) actually state in their ToS that you must include an OSI approved license in your repo.
Well, no, If you publicly release the source code to your proprietary software, people can download it and tinker with it, so long as they don't distribute it whether it's modified or not.
Unreal Engine, for example, has its entire source available free of charge online, but it's proprietary software and you can't make changes or use it to make a game unless you obtain a license from Epic Games (which is now free of charge in many cases, but you still have to go through the process of getting it).
Even if there's an option that says "proprietary", I'm OK with that...
It would get rid of all the ambiguity of stumbling upon a very wonderful project but being unsure if you can use it due to no explicit license.