Logistical reasons . Modern warfare is fast and hard . Tanks don’t fit that bill . They require a vast logistical chain to keep them moving .
Also the devoplment of TOW , missiles mean a tank can be taken out from well over 5kms away .
It’s a bit like the battleship era . Styles of warfare move on and some kit just isn’t suited to the new style .
IFV’s are cheaper , faster more mobile , can carry men and don’t require so much logistics . And now with the devoplment of missiles and auto cannons , they can do the job just as well .
Also with the world devolping the way it is woth large cities etc , warfare is becoming more urban , so a tank becomes redundant . Better to have a fast moving IFV .
Personally I love tanks
they make an impression on the battlefield a IFV simply won’t ever . The screeching of the tracks , the sound , the vibrations it raises moral hugely even in excersises