#2 Teams have found a counter
The three at the back system was brought in to counter the threat posed by the conventional 4-3-3 or the 4-2-3-1. Though it worked a charm in its initial stages, other teams and managers have now found a way to counter it.
The easiest and the most sensible counter to a 3-5-2 is to play a similar formation yourself. With the wing-backs cancelling each other out, and the midfielders not outnumbering each other, the game would assume the look of a chessboard, rather than a football field.
On many an occasion last year, Chelsea couldn’t find breakthroughs against teams playing a system similar to them. Hence, they committed extra men forward and got their fingers burnt by the fire they started themselves.
With a seemingly obvious counter available, managers have started to move away from the three at the back system to the conventional ones.
However, there isn’t anything to suggest that the three-man defence would never come back into fashion. Just like many things in life, football also goes through cycles and this system would again come into vogue when the four-man defence becomes prevalent. Till then, one can expect a switch to the conventional systems this season.