An age-old issue with FIFA that as to do with the dated game engine. The player positional logic in FIFA is designed for wide-open play: lots of goals that way plus the game is meant to be a simple and fun representation of the real sport. That's why you'll mostly see 4 defenders taking on 2-3 attackers with the rest of the 13-14 players standing around upfield watching. Midfielders barely ever join in the attack, and as for defenders... fuggedaboutit.
The good news is the line sliders go a long way to help change the positional logic so as to create a more realistic and team-inclusive football experience. I play on Legendary, so I use a very defensive line slider setup. The CPU always starts games like gangbusters, so I start the game with my height and length line sliders at 0. This forces all my players to come back to my box to help defend. Here are a couple of examples of how changing line sliders changes the positional logic:
