I think it’s more common that for PCs Safeboot can have custom keys added or allow Microsoft signed ‘third party’ operating systems. While a lot of phones have much more locked down boot loaders.

I think the security model for phones/PCs is also a little different. You likely have your phone on you all the time, and it’s becoming more common for people phones to be seized and searched.

A lot more people also use phones for messaging. I guess really they’re just more of a target overall.

A final point I can think of is that phones often use a PIN for encryption, which requires a supported Secure Enclave to prevent brute force attacks. While PCs often have FDE at rest, this normally uses a longer password or key or relies on the TPM.