Why would they care now? Their devices are essentially dead in the water in western markets.

Check out the double digit growth they have in the EU.

Google is fighting hard to keep their app store on Huawei devices, because they don't want 10Ms of users to force-adopt alternative app stores.

why would carriers care about bootloader unlocks? it's different from a carrier lock, which prevents a phone from being used on another carrier.

Doesn't an unlocked bootloader almost automatically allow bypassing of the carrier lock?

if allows baseband chip firmware update, then yes

aren't those signed anyways?

even if it is, you can probably do an update with an unlocked one. (so the update is not device specific, not tied to IMEI)