Because they still retain copyright over the code. They've merely granted the Linux kernel a right to use the code under the GPL. They are with their rights to rescind that license.
Which I think is a mess because of how that reaches out. It may also be another point in favor of the GPL just being a bad license. If I rescind the GPL on my code, then everything that depends on it needs to rewritten and there may be things that aren't aware they're using my code that needs to be rewritten.
Then what about if someone modified my code? Then where does the copyright lie?
I tried doing that on my wikipedia contribution after being bullied by a sysop, my plea was ignored (actually removed from public view) and received a permanent ban from all wikimedia project instead, probably to ensure I could not keep asking for this. I was told creating such a precedent could collapse the whole wikipedia and that it was too big a money maker for them to let this happen.
I lacked the financial means to enforce my rights in court so I dropped it and moved away from spending 10-14h a day contributing to wikipedia.
The kernel is probably not as corrupted as wikipedia management is, so they may allow for rescinding GPL if asked but would that prevent the removed code from being added again rewritten or not? Could the original author sue for copyright violation ?
The kernel is also used by 1000’s of companies that would now be open to lawsuits so you don’t even need money for a lawyer law firms would jump on the opportunity to sue Google or Amazon.
The way the US does things is not necessarily how the rest of the world does. A non US citizen has exactly 0 right in the US as I've been remembered when I got scammed by a us reshipper service who unilaterally decided to keep my belongings.
GPLv2 is not the only license without an explicit "no-take-backsies" clause, and pretty much all literature I've read about open source previous to this incident suggested that although you could relicense future versions of the code, you couldn't put the genie back into the bottle on old releases.
Also, to be frank, I think that if there _was_ settled law saying you could rescind old licenses, it would have far-reaching ripple effects throughout the open source world. Let's be clear, it would be a weapon that could be used by any slighted maintainer or former maintainer to damage a project, for _any_ reason. And if a single or group of maintainers could do it, a corporation with dollar signs in its eyes could do it just as easily. Be careful what you wish for.
