wuseman
Why would they do that?
That's up for debate. Some could argue, that since Google decided to stop promoting the Pixel phones as reference hardware, there would be no need for it to have an unlockable bootloader.
Another point is, that Google might be pressured by law enforcement, to prevent the use of custom OS'es that can't be unlocked with off-the-shelf forensic tools like Cellebrite. Even exploiting the OS is proving to be difficult with GrapheneOS's exploit protections features. You can imagine that law enforcement is not happy about that and I wouldn't be surprised if that was at least a partial reason for the decline of custom Android forks.
All in all, the market for phones with unlockable bootloaders is extremely small, globally. It doesn't hurt Google to lock down their hardware; after all - it's their right to do, what they want. When you look at other manufacturers (Samsung, Huawei, Xiaomi), you will see the exact same patterns emerging. So I guess Google will go that route some day.