As has been stated before, the problems with those "solid tires" that include the "tread" are:
--no proper bead, so they can just roll off the rim under side-loading (this is why they go on so easily--they also come off easily). Could cause spectacular crashes when this happens in front wheels during a hard turn at an intersection with traffic at speed, especially if the tire jams the wheel in the fork.
--usually no proper "carcass", so the "tread" wears down very rapidly into the soft foam core, *or* they are the same foam core all the way out to the tread and they wear VERY rapidly under anything other than child's use or intermittent use.
--not available in many types of tread, so you're stuck with whatever kind they sell, rather than ones actually useful for your type of terrain/roads/etc.
FWIW, it is not impossible to get the foam-tube types off intact, when using regular tires with good beads over them--it's just very difficult.

I did this once already with DayGlo Avenger due to a toasted rim, and traded out the MTB tire the wheel came with for a better-suited Kenda Krossroads type with road-slick center and knobby edges. (the Kenda tire is actually one I could no longer use with air-filled tubes, as it has sidewall damage that would herniate with air-filled tubes and rip the tube open on the brake pads, but with airless foam tubes there are no such problems!).