The Cloture Rule is just a rule and such is modifiable with a simple majority (>50%) and has been rather recently so that judicial appointments could be made without needing 2/3 to override a filibuster. If Democrats wanted to actually govern without needing 2/3 of the votes in the senate they could've; however, much like the Republicans they aren't actually a homogenous block so removing the Cloture Rule would just demonstrate they aren't in agreement and look embarrassing (akin to Republicans not being able to agree on a speaker of the house).