Because they were trying to fix one problem and introduced another. Thinking they were keeping some happy but in turn annoying others.
You can't keep everyone happy.
And what is the "airspace normally used for approach and departure"? What I might think is normal, and be on frequency, might be different to you. You go sailing through said airspace thinking your not in the way, but in this case you happen to be in my way? If I really wanted to I'm sure I could conjure up and cherry pick some specific instances to support this case. Similar to you picking your examples to support your viewpoint But I really cannot be bothered.
I understand what you are getting at, and there are pros, but there are also cons. Much like the 20nm radius CTAF.
Whether we keep the current system, or change to yours, do you think 100% of users are going to like the system? No.
And they won't dislike it just to spite you, they'll just dislike it.
Don't get me wrong, I'm not "anti change". Can our airspace and ATC system be better? Yes I'm sure it can, and I have my own thoughts on other unrelated conversation topics here.
Can the US system be improved? I'm sure it can.
But I'm not sure that your proposed changes are what the masses want. If it was, don't you think there'd be more support for it? Change isn't necessarily good. Remember part 61? Industry is still struggling with that!