I'm honestly not sure (I haven't played with modems much), but I do know that doing a clean wipe of the eMMC or an SD card is way easier than a clean wipe of your modem. It's also a fair bit harder to check for anomalous activity, although with easier shell access, maybe that mitigates both problems?

To be clear, I think it's a lose/lose situation, because I want access to the modem in my pinephone, but I'd rather shell access require some kind of physical attestation (serial connection over the pogopins or something), instead of ... this.