Edwards Snowden just made a tweet with final warning for everyone that privacy for Bitcoin is needed on protocol level.
I tend to agree with him on this and I really don't understand why nothing has been done regarding that for years, unless this was done intentional.
I don't know enough to be called a 'developer', but I think you're just totally underestimating how difficult it is to achieve this without potentially fucking up the entire protocol. Bitcoin is already gigantic enough that we can't afford to move fast and try to just push upgrades under the sun.