Why is a Memory Care facility asking for 3 years to be paid up front in cash?

This is not normal. There is usually is a fee to move in and first months rent. Are you sure they want the money up front and not just proof the money is there? This does not sound right. Find another memory care.

I couldn't say, but I sure wouldn't be paying it, either.

I would not just walk away from this place but run!
I can not imagine paying any rent up front and in cash no less.
(I doubt many people are walking around with that kind of cash anyway.)
Start your search again.