It's 'Pride'. They made a decision and are sticking to it regardless of peoples reactions to it. They have used every excuse they could think of to not implement something along these lines. Fdev were asked by a brave brave soul during a live stream about PPBs (player planetary bookmarks - yeah you're right the acronym sucks PAPBs?... anyway..) I was told there wasn't a compelling immediate need for them... Since that statement we have had a lot of 'things' and much 'stuff' added to the surface of planets, and yet there are still no announcements of PAPBs ( am going to keep using this until someone thinks of a better one. It's my choice and I'm sticking to it

)
So possible reasons for not adding such a system:
It's beyond their skill to do so.
It's about "progression". You're own skill progression.
They honestly don't see it as a problem or issue.
Pride. Stubbornness, call it what you will.
It's not PewPew.
Yes there is a significant bit of tongue in cheek there with a few of those reasons. It's certainly not out of their skill set to create such a system, and make it good. As for the others well I think it's a mixture of them really.