If the modem is certified with carriers, why won’t they activate SIMs?

[desca]

You give a carrier or MVNO your IMEI, where the first 8 digits are a TAC that identifies the EG25-G, and the next six digits are just some sort of serial number (I think), and then a checksum digit, and rather than saying “Oh, the Quectel EG25-G! A fine piece of hardware! It’s been certified by the carrier, has a VoLTE profile, etc., so you’re all set, and enjoy your service!”, they say “Sorry, we can’t help you.” — so most people having to activate their SIMs in other phones.

What am I not understanding?

And is the situation likely to improve in some way over time, or is this just life for PinePhoners?