Broadly maybe the viewers are just getting sick of all of the shilling for cheap shit that goes on with the ever increasing sponsor segments so many channels have these days. Arguments will be had about just how needed all of those marketing dollars are for the creator to keep doing their thing vs them getting used to a lot of money and wanting even more of it. But the end result is a worse viewing experience for the consumer. I know there are a lot of channels that make good content that I've stopped watching because they spend a quarter of the video shilling junk. Sure sponserblock would get rid of those sections, but it won't send a message like unsubscribing and stopping watching them completely will.

Also maybe this is a larger Youtube usage hit due to their aggressive anti-adblock nonsense and uptick in ads and shitty UI design.

For Linus specifically, he has the above issues as well as having been very publicly outed as a slimy deuce. What his channels put out is not unique enough these days to justify dealing with the shilling and his companies bad behavior.