two main reasons.
* LTC didn't activate SegWit for capacity increase since it never needed that part. it activated SegWit for many other benefits.
* there is no fight over power in LTC but there is a big one coming from the BU camp trying to take control and that is why they are stalling.
why did litecoin decided on a 50% vote while bitcoin had to go for a 95% vote?
no the threshold was 75% for litecoin not 50%. and as other poster said the support went above 95% and nearly was 100%
If SegWit2X is activated will UASF be dropped?
it depends on many things actually, but since SegWit2x and UASF both will reject non SegWit blocks and SegWit2x is activating SegWit i think it will (i am not 100% sure though). as i said it depends on many things like if they continue signalling for SegWit to the end or will they change their position, or are they going to use the same bit version for it.