They are roughly 6 ppg different right now, AKA, the difference between getting into the end zone or not.
MIN has leaned early on its rush game and tends to have lower-scoring games with fewer possessions than CIN does. Chase also has quite a bit less target competition than Jefferson does, as a large body of the passing work has gone to Addison and Hockenson. Those two combine for as many targets as Jefferson has; CIN's next 3 pass catchers don't combine for the targets that Chase has, on top of that offense passing a much, much higher amount.
There's not much in the way of helping you if you drafted fantasy players without considering the situation around them. MIN was never going to be a "throw 50 times a game" offense this season, and even then, Jefferson still has very good receiving stats -- he just doesn't find the end zone. Nor does the entire offense, it's not a 'him' problem (it actually looks like Jefferson is slightly better on a per-target/per-reception basis, looking at the stat page, but again, lack of TDs).