It's confusing to me that you're calling it "less-constrained." The signed-bootloader world really caught fire in SoCs like Snapdragon and indeed the 410E and 600E include SecureMSM/TrustZone. It hasn't (yet) found big popularity in x86_64 designs -- even when the processors offer it many customers don't leverage/enable it.
The "locked down" designs come from two big motivators: DRM and security. Since many snapdragon phones are sold with subsidies, the signed bootloader allows the network operator to restrict the phone's "owner" in various fashions. The security provided by a signed bootloader is real -- it's much harder for a malicious actor to create ransomware that targets mobile phones like they do PCs.
I'd expect/hope that you can decide not to opt-in on the Snapdragons' SecureMSM features, but it doesn't seem any "less-constrained" than Intel or AMD's offerings.
The "locked down" designs come from two big motivators: DRM and security. Since many snapdragon phones are sold with subsidies, the signed bootloader allows the network operator to restrict the phone's "owner" in various fashions. The security provided by a signed bootloader is real -- it's much harder for a malicious actor to create ransomware that targets mobile phones like they do PCs.
I'd expect/hope that you can decide not to opt-in on the Snapdragons' SecureMSM features, but it doesn't seem any "less-constrained" than Intel or AMD's offerings.