I see the first problem all the time, especially at stoplights. Often when there is a line of cars waiting at a red light, when it turns green someone will remain stopped so that a waiting vehicle on a perpendicular street or nearby business can pull onto the highway in front of them.
They think they're being polite, but they're forcing dozens of cars to wait for an additional cycle of the stoplight, whereas if they had just pulled through the light as normal then the waiting car would get a chance to merge as traffic either cleared or came to a stop again.
"dozens" is quite a bit of hyperbole. I generally only see behavior like this when traffic is dense and the speed of traffic is limited. In those cases, letting someone in doesn't decrease the number of cars that make it through the light. Additionally in those cases, it's quite possible that if nobody lets in the the car trying to merge, they will never be able to merge.
Obviously, optimal behavior is dependent of the traffic conditions.
"Dozens" is not hyperbole at all, my account is an accurate and truthful statement of the traffic conditions in my area and the consequences of those bad actors.
Cars looking to merge should do so as the traffic comes to a stop. A car already on the highway they are looking to merge onto need only stop sooner than they otherwise would, allowing them to pull out into traffic that is already at a standstill.
I'm not sure I understand the traffic conditions you are describing.
Lets take "dozens" to mean "atleast 18" (a dozen and a half). The average car is 15ft so this means to fit the 18 cars bumper to bumper there will need to be at least 270ft between the car you let in and the car in front of it when it passes out of the intersection.
If you leave half a car length between cars and allow the full 2 dozen this number quickly becomes 528ft.
If people are really this slow in pulling out, I feel your pain. However it is these numbers that caused me to judge your anecdote as hyperbole
Additionally, you suggested blanket solution sounds more dangerous as well as completely unworkable in bumper to bumper trafic:
"Cars looking to merge should do so as the traffic comes to a stop."
It's far more dangerous to pull out in-front of a moving and already braking car that may or may not see you then to pull out in-front of a stopped car that has indicated that it does.
I see this too, in the bay area. There are so many intersections with green left-turn arrows that drivers forget the rules when they encounter a regular light without a left-turn arrow.
The particular case is that a driver going straight will yield to a driver approaching from the other direction who wants to turn left across them. They should not yield. They have a green light.
They think they're being polite, but they're forcing dozens of cars to wait for an additional cycle of the stoplight, whereas if they had just pulled through the light as normal then the waiting car would get a chance to merge as traffic either cleared or came to a stop again.