One of the main reasons bathroom floor tiles crack is if the floor is not stiff enough to resist bending slightly when walked on. Preventing this can require installing the tiles on top of either ¾ inch waterproof plywood over the existing subfloor, or plywood with another layer of cement tile backer board. Older houses (or high end new construction) may have an inch of actual cement between the sub flooring and the tile.
Another problem can be that the tiles are too large. If you look in many older –pre 1950 homes- the bathroom floors are made up of a large numbers of very small tiles often less than two inches square. Today many contractors and homeowners prefer large tiles that may be as big as 12 inches square. Larger tiles are much much more likely to crack. If a floor with small tiles does flex slightly, the cracks are most likely to happen in the grout between the tiles which is easier to repair, and harder to notice.
A third problem is that your contractor used wall tiles rather than floor tiles. Wall tiles are much thinner.
However, any properly- installed tile floor should easily be able to withstand the ordinary water that gets on a bathroom floor.