This is simply not true. Many high range MTB tires are specifically designated for front or back usage, and practically all tire reviews mention that.
Certain manufacturers have encoded the "front/back" purpose of their tires in their names. Maxxis Minion DHF is meant for front, while Maxxis Minion DHR is meant for the rear. Of course, many people use them differently, depending on their riding style and riding conditions. It is not uncommon to see a "front" tire at the rear, for example.
Tire thread designs have changed somewhat over the time (but so have the bicycles). It is unusual to find tires with the "angled" profile (
>>>>>>>) as your pictures show at the higher end of the market, where the rear/back distinction is important.
Modern gravity tires are all more blocky (
▓▓▓▓), cf. Schwalbe design, but others look quite similar: