Norris had already replaced him as the primary catcher, and after they got Kottaras they dumped Suzuki for salary relief.
Flores has been in a major slump for the last two months, both offensively and defensively.
I'd say he has been slumping since about April 5th, you know, like all season. The injury really set him back and he is a backup catcher now. Nothing else to it. It is a shame to see it happen, but Ramos was definitely the starter even in a bad year this year before he got hurt. Solano and Leon still have lots to learn behind the dish in blocking and fielding, but Solano could actually hit and Flores hasn't hit and aside from the decent blocks (not great because maybe three of Henry's crazy pitches should have been blocked by him) his defense is terrible, i.e. his arm is not what it used to be.