The team behind GrapheneOS want it to be really secure so they have specific requirements that the phones from Fairphone sadly doesn’t meet.

For a phone to meet all of these requirements AND still being everything that a Fairphone is would make the phone more expensive than the average consumer would be willing to pay. I know several enthusiasts (me included) that would pay for one, but there are simply just to few of us.

eCall, alarm systems, elevators and many types of sensors.

2G should die though. You can use the frequencies for 4G/5G to get better reception.

And if the thing depending on 2G has the space for it (like a car or an elevator) then the thing can be upgraded with hardware that supports 4G/5G.

…Unless the manufacturer is a dick and wants you to buy a whole new thing. I suspect that this will happen a lot.