[snvzz]

Because it is more profitable for smartphone makers if you need to buy a new one.

Unless there's legislation to force them to allow enrolling new keys or otherwise disabling secure boot, the abuse will continue.

[realusername]

Third party roms also do not include all the bloatware and spyware they are loading into the phone, they aren't a fan of losing control.

[wolvoleo]

** Spyware and bloatware that they are being paid to load onto the phone unfortunately

[EgregiousCube]

This is true; there is additionally a valid argument that there is security benefit to locking down the bootloader. I don’t like locked down bootloaders, but I get the argument.

[drnick1]

Yes, locked bootloaders secure the profits of the manufacturers who want to run crapware on your device for their benefit.

The hardware is theoretically yours but they won't allow you to use it in the way you want, it's shocking.