The main issue is carrier relationships. Not patents.
The modem is not the hard part, not easy either. But having enough engagement with carriers worldwide to support all the use cases in terms of infrastructure combinations. The validation process for that is extremely expensive. That is one of the value propositions Qualcomm offers to the customers of their chipsets; they basically take care of all that headache for the phone vendor/integrator if they just go with their chipset (android) or modem (apple).
This is why the most successful modem companies (Qualcomm Huawei) either also offer a lot of infrastructure products themselves or have very strong connections with infrastructure manufacturers like Ericsson and Nokia (Samsung, Mediatek).
From the HW perspective, the issue is not the modem itself, but all the supporting chipset specially the antena/RF elements. Which in 5G involve a lot of beam “herding” whose power is hard to scale and are not that easy to manufacture. Also there are lots of thermal issues with those antenna elements.
Apple does not have, currently, the corporate culture for that type of engagement. Because they got a very good technical team from intel, but not the other side of the equation in terms of telco carrier infra engagement.
Because there is no need from an address space or compute standpoint.
to understand how large 128bit memory space really is; you’d need a memory size larger than all the number of atoms in the solar system
In the rare cases where you need to deal with a 128bit integer or floating, you can do it in software with not that much overhead by concatenating registers/ops. There hasn’t been enough pressure in terms of use cases that need 128bit int/fp precision for manufacturers to invest the resources in die area to add direct HW support for it.
FWIW there have been 64bit computers since the 60s/70s.