This entire attitude around denying attribution is unreal. I see it in industry all of the time, especially now that I'm in gamesdev. People pull out all of the stops to prevent certain people or even certain disciplines from receiving credit for their efforts. It's abysmal.

That is an excellent question. It may well be that even single line drive by patches raise to the bar of being a kernel contributor, it may be that most of the authors of such small patches have historically had a better idea of their place in the greater scheme of things and that what matters is that the bug gets fixed (it's a security issue, after all) rather than that it gets fixed in their way or with their name affixed to the patch.

Fixing bugs is a contribution, and detecting bugs and doing RCA is also a contribution. In this case the OP got credited for the second and the third using the appropriate mechanism. The maintainer could have used another tag to add additional credit, but chose not to as is their right - and custom with such small patches, especially if they need work.

High profile projects such as the Linux kernel suffer from attracting people that just want to be associated with the project, I think OP went considerably beyond that and deserves some credit but does not have an automatic right to a particular kind of credit and if that was his expectation he should have ensured up front that that was the outcome. By posting an incomplete patch for a security issue to the kernel mailing list this was the expected outcome, in fact the maintainer spent considerable time on back-and-forth with the OP.