Because in defensive situations 2 MCs of 4-4-2 become DMCs. That's how 4-4-2 work even in real life. In top eleven you can't score many goals vs 4-4-2 no matter how good you can be. Best way to break it is from flanks.
You can try it but it never worked for me putting AMC against 4-4-2.
I play myself 4-4-2 and I never put DMC against AMC and defense work fine.