I cannot explain why "ALL" the local operators would ask for descent to 2000' as this makes flying a continuous descent more tricky. Maybe they are choosing to fly level at 2000' and intercepting the 3deg approach path.
Being initially cleared to 2000ft on a RNAV approach doesn't mean you have to fly a level segment at 2000ft. Just like with being vectored for an ILS approach. If you wish to fly a CDA then there is nothing stopping you in doing so.
I'm based in DXB and for the fleet I am on at least, there is no procedures that prevent us from flying a CDA on an RNAV approach. It's how most guys will fly it anyway as it makes life easier.