He's tired. He's older. He mentioned several times how he's been developing this for decades. Maybe he is making a balance, maybe he thinks that the Kernel does not really need him so badly now, and he can take a time out.
If all of those things go in the wrong direction, Linux could lose its reputation. For example, imagine a new vuln discovered and Linux failing to fix it for more than a year, or imagine Linux becoming slower than other alternatives in new processors