Yes, yes, we know that. We also know that in 2009 when 2.0 RC2 first came out, a lot of hosts were still very firmly using 4.3. Even now, I know of production sites still running on 5.5 that for one reason or another cannot be upgraded, so it's really not that simple.
They're also not duplicates; every single bbc definition has its own create_function instance. Also, no, it wasn't deprecated in 5.2, because it couldn't have been deprecated until its replacement came out the following version. It has been deprecated in 7.2, which is only out in 2017.
Part of the problem is that people like you demonise the SMF team - if they spend time on 2.0, they get blasted for not finishing 2.1, and if they spend time on 2.1, they get blasted for not sorting this for 2.0.
It's that kind of attitude that has led a number of people not to contribute to development, and for those few brave souls that do, they have to do it in their evenings and weekends around their day job.