I would guess over watering.

This is what a healthy pineapple looks like:

I grow right into brown dirt and yard soil. In the pineapple plantations they do the same. No sand involved.

You've also got a pineapple fruit so time to harvest?

I don't know. I doubt it's the sand. I am curious to know as well. Have you grown pineapples before that got bigger than this?

No experience with pineapples, but when a plant starts looking like this it's often either too much or too little watering. Does the pot have an unobscured drain hole in the bottom? How did you choose a once-every-three-days watering cycle? (That sounds insufficient for outside growing this time of year to me.)

That fruit looks great for a tropical plant growing way up north!

The issue is not the sand. Top dressing with sand, mulch, rocks, etc is a common practice with potted plants that at worst does no harm.

My guess is over watering is getting to it. Try just thoroughly soaking it (as in watering until some starts coming out the bottom of the pot) ~ once a week. The idea is to let the soil dry out a little between waterings. You can always stick your finger into the soil to see if it is still damp to see if watering is needed.

I have dozens of pineapples in my (very sandy) south Florida soil and this looks like a drainage problem to me. Either the roots are having too much trouble growing into the soil, or there’s too much water.

I'm about as far away from you as it's possible to be & still be in the Continental US, but a couple of things. Pineapple I hardly water at all, have it basically in orchid mix (my yard soil is atypical for Florida, very rich and damp) and they don't absorb much through the roots so if you are trying to fertilize it or give it minerals, spraying diluted fertilizer on the leaves will work better than putting something in the soil.