Mobile phone makers always lock their device's bootloader - that is, they prevent you from getting root access to your device, or uninstalling the default operating system and installing something else. There are ways to unlock the bootloader, but you have to jump through hoops to get it done (difficulty varies by brand, up to being impossible).
Meanwhile, the bootloader of a PC always come unlocked. You can insert a USB stick into a brand new device (no extra steps required) and install whatever you want. I do not own Mac devices so I may be wrong, but I heard that Mac bootloaders aren't locked either; that's why Asahi Linux is possible.
It makes every sense for PC makers (and Mac if I'm correct?) to lock the bootloader just as phone makers do, i.e., to control what softwares could be run on their devices thus maintain market share. Why don't they? It makes even less sense when many PC brands also make phones, but their PC comes with the bootloader unlocked while the phone is locked. Why is there this disparity?
Are there financial incentives for companies to keep their PC's bootloaders unlocked (e.g. corporate customers)?
Are there legal requirements that PC bootloaders must not be locked (e.g. antitrust laws)?