Because they are Fun! Because many of us have fond memories of them. Especially at time when Models were just that. Model Cars. Toys! Not Replicas. Not Scale Reproductions. For those times, (as an Child or Adult) you did not know or care, about exact scale fidelity. Truthfully, I think the Switchers kits look better than many of the old AMT '32 Fords, any way. And the MPC Fords offer some great engine and wheel options. There is a Joyfulness in the Switcher kits, that no Model today will ever have or attempt to attain, with today's Adult Oriented Marketing and Budget Constraints.
Lastly because many people like them, and I suspect not all of the people who like them today, are the folks who built them when they first appeared in the 1970's.