God knows! As Jype alluded to, Kepa isn't great at saving shots from distance. If opposing players see him in goal, they might as well try their luck and try to get a strike off.
And why did Tuchel want to give the cup keeper more minutes? Because it was Kepa? Would Tuchel have done the same had it been Caballero instead?
Compared to yesterday, I don't think anyone really blamed Kepa for that Arsenal loss. That was all on Jorginho and Zouma if one looks deeper.