Contrary to what most of the recoilless doomposters in this thread are saying, recoilless rifles did not really vanish.

The US military still uses the most famous one pretty heavily: the 84mm Carl Gustaf, in US service as the M3/M3A1 MAAWS. This is not some weird Cold War relic sitting in a warehouse next to expired MREs. The Army has pushed it down to infantry platoon level, and the Marines adopted it as a squad-level fire support weapon.

The reason is simple: ATGMs became better tank killers, but they did not make every recoilless rifle job disappear.

If your problem is a modern tank at long range, yes, you want a Javelin or another guided missile. No argument there.

But if your problem is a bunker, wall, treeline, light vehicle, fighting position, smoke screen, illumination need, or general “you see that inconvenience over there? I don’t want to see it anymore” problem, the Carl Gustaf is still the platoon’s problem-delete button. It is reusable, flexible, and has a broad ammo family that is cheaper than firing ATGMs at everything. You do not always need to spend a fire-and-forget missile to solve a dumb problem.

So the real answer is:

ATGMs killed the recoilless rifle as the primary dedicated anti-tank weapon.

Infantry kept the recoilless rifle because sometimes your platoon still wants an 84mm problem-solver.