Software only would be a pain in the ass for switching a SIM between my iPad, IPhone Max and Mini as needed. There is no reason to fix what is not broken.
Software doesn’t have to be a pain in the ass for that. It would be quite easy for the software to allow the same SIM to be installed on multiple devices and only active on one at a time. Reasons it hasn’t happened yet aren’t due to technical difficulty. (Potential security issues, relationships with carriers, etc. are the hold up)