AI labs are buying operational data at high prices. Nobody is buying source code because it is so easy to get it off GitHub and similar platforms. I wonder whether labs would want to pay for using source code if people host their own version control systems.
Not it won't, source code itself is generally useless for most implementers who want to actually use the software rather than experiment or hack around it. Most of its value comes from business workflows, configuration, support, training, etc. around a software. Besides, github isn't the only hosting forge in town, plenty of others like gitlab, bitbucket, source forge, codeberg, etc. exist and those will keep serving as a marketplace for code and ideas.
Maintaining systems is where the costs are at. That is also where the profit is at.