Cork Flooring

[Slipknot]

installer might have laid the tile with sanded grout or the thinset was not modified or old or not mixed right.
In any case, tear them out and put down something else like you plan to

it is probably on plywood subfloor

[nightfighter]

Yep. Sounds like they used thinset mortar. If they did not wet the plywood, the water would have been sucked out of the mortar mix by the wood before it cured, leaving the sand and no adhesive.... Demo should be fairly easy.
Break up the tiles with a two or three pound hammer and then use a floor scraper. Then check to be sure subfloor is really fastened well to the joists. See if the floor is crowned. (use a marble) If you want to re-tile, screw down 1/4 inch sheets of hardibacker and tile on that. Just be aware you are raising the floor level so watch your thresholds and doors, if any.