Or their mainstay MBT's have suffered such great losses (more than 1300 T-64/72/80/90 lost) that they have to take out these old tanks out of the storage?
Dunno, but perhaps this may just be the case
Or maybe they have sold out and cannibalised their more current designs like T-72/80 during last 3 decades, so they now have no enough of them ready for activation, while T-62s were mostly not so hot commodity...