I see it often too, just the other way around. Most cars are doing about 120 km/h (which is the speed limit) and some people are overtaking them at 140 km/h at least. They don't know about velocity matching nor speed limits.
Overtaking at a significant speed difference is ok. However, when you want to join another lane, you should match velocities, not force everyone else to match yours.
Replying to the grand-parent:
While we're talking about driving.. what the hell are they teaching new drivers these days, that they don't know you're supposed to match velocities with the rest of the traffic when entering a freeway? I'm serious, they're getting on a freeway that's humming along at 70-75mph, and they're doing it at maybe 60mph. I see this every single day, too. Do they think they're going to break their cars or something, if they stomp the accelerator pedal?
A while ago, I was watching a video from a trucker, who was also mad at idiots not accelerating on the onramp. In the comments, a person just having gotten his driving license spoke up and said he was trained to gently accelerate when joining the freeway, to save fuel.
Apparently, the trainer never considered it saves much more fuel when the truck coming up from behind doesn't have to brake and accelerate again...
Disclaimer: what I described happened in Germany, with a truck speed limit of 80 km/h, the person merging doing maybe 70. (70 km/h == about 44 mph)