Yes, and remember too that SIMs are standardised technology from the mid-1990s, originating in GSM. It's not a trivial matter to change security in globally standardised technology.
(and Even if you did, it would need to be backward-compatible and still support SIM cards)
There is a good deal more to telecoms tech than just the tech side - the standardisation process brings a whole bunch of competitor companies into a room to develop a solution, incrementally over a number of years.
This applies from physical aspects all the way up to higher level concerns like security. It's a fascinating development process.
