a) It seems unlikely that you can standardize the battery form factor between different models. You'll still have a handful of different standards between small, full size, and truck/suvs, and semi truck forms. It's been hard enough getting manufacturers to standardize on a single charging port. Battery form standardization would be another order of magnitude hard.
b) Even if you somehow manage to do it, you're forever stuck on that form. Limits the experimentation and flexibility you have to develop for new use cases. Upgrading battery tech, like Tesla's switch to the bigger and more efficient 4680 in the cybertruck, would also get added friction since it wouldn't be compatible with older standards.
c) Tesla at least is starting to turn the battery pack into a structural element to reduce mass. Unlikely you can do this and be swappable at the same time.