It's a relic of the cold war that everyone seems to have a completely unrealistic and romanticized view of. Yes it's a heavy slow plane that was designed around a massive gun. But that gun actually isn't very effective against modern armor.

The A-10 could not penetrate the T-62 from the front, let alone the better armored T-72. For a gun kill, it would need to attack from the rear, but that would put it at significant risk to soviet anti air. The solution was to use a Maverick missile against armor.

There are now far more effective planes to lob missiles at armor. All while staying high and away from danger. The A-10 also was not designed with MANPAD's in mind, because they didn't exist then. Even if they do survive, there is down time in having to repair the platform.

In a cold war gone hot scenario, the airforce estimated that they would have lost all of their A-10's within 2 weeks of conflict.

For the CAS mission an Apache would be just as good. 16 Hellfire missiles along with strafing with a 30mm chain gun throws a hell of a punch, all while being slow enough to accompany ground troops.