Because they are too strong. They leave little counter-play.
It is not healthy to have thieves with this kinda of mobility and evade frames in anything other than PvE.
The ability for Halos/Weavers to do this much burst damage in the time to spam out a quick MACRO is also not healthy, for anything other than PvE.
We know u can disable skills and 'hotfix' things when enough 'complaining' is going among the masses (looking at you C.I.)--well, fix this!