This type of left turn is less an "asshole thing" and more a "drivers compensating for poor design" thing.
Typically, the "Pittsburgh left" is used in places where there should be a protected left turn as part of the signal cycle, but there isn't, and at times of high traffic flow it's the only way for any traffic to complete the turn (since waiting for oncoming traffic to clear on a green essentially means waiting until the multi-hour-long period of high traffic is over).
The usual case for this is a light where left-turning traffic must wait for oncoming traffic to clear, but at certain times of day oncoming traffic never clears. The only gap in oncoming traffic occurs when the oncoming traffic has a red light. But the left-turning traffic also has a red at that point.
I thought we were talking about the Pittsburgh-left. That's not what you're describing. The Pittsburgh-left occurs immediately after the light turns green, when both the oncoming traffic and the person making the turn have a green light.
My point was, why do you need to do that when you can just enter the intersection during the green light and complete your turn once the light turns red?
Having driven in the single lane thoroughfares of Pittsburgh, I’m grateful for the people in front of me that take a “Pittsburgh-left.” Otherwise the entire lane would be stopped for every left turner each green light. This way it’s only stopped for every other left turner in the cases where a left-turner ends up in front of the line. It’s an improvement to everyone’s traffic flow.
Driving in California, the best roads literally make it illegal to turn left during rush hour when the intersection doesn’t have a left turn lane. People still get where they’re going.
Whether you do it after the light goes red (illegal) or immediately on green (also illegal), it's the same underlying problem: the intersection needs a protected left turn in the signal sequence.
In many places it's illegal to enter the intersection (even if the light is green) if you're unable to immediately leave it, mainly to ensure that intersections don't get blocked if there's a traffic jam in the direction you want to go; and this rule also prohibits (not everywhere) to enter the intersection for a left turn if you can't complete the turn right now because there's still oncoming traffic.
Then the laws in Pittsburgh are just bad.
Not a design question at all.
Here you oull into the intersection on green, turn slightly ti a big white cross on the road for exactly this purpose and go when it is clear.
This happens when the oncoming side has red, but before the crossing cars have green.
The time between red and green is long enough for all two or three cars to clear the intersection.
The only gap in oncoming traffic occurs when the oncoming traffic has a red light. But the left-turning traffic also has a red at that point.
Which is why you need to move onto the intersection as the light turns green -- you've now passed the traffic light, so once the oncoming traffic gets the red light, you are clear to turn.
Typically, the "Pittsburgh left" is used in places where there should be a protected left turn as part of the signal cycle, but there isn't, and at times of high traffic flow it's the only way for any traffic to complete the turn (since waiting for oncoming traffic to clear on a green essentially means waiting until the multi-hour-long period of high traffic is over).