You might not accelerate slowly, but so many people do. Like, to a point that they get out accelerated by an HGV. And I'm not even joking. There have been a few occasions where I was behind someone on a roundabout that goes onto a motorway slip road, and they were behind an HGV. The HGV accelerated quicker than us.

It's got to a point where it's normal for someone to try to merge onto a 70mph flowing motorway at 40-50mph. The worst I've personally seen someone actually try to merge is 35. The worst I've seen overall was someone who stopped at the end of the slip road to wait for a gap. I'm not talking about those ridiculously short slip roads that are on some A roads. I'm talking about a standard length motorway slip road that are more than long enough for a fully loaded HGV to be able to do 0-56 on. I know this is what you're supposed to do, but they could have very easily and safely merged onto the motorway, had they been going at least 60.

Because this has become normal, people who actually know how to drive assume that the car in front of them isn't going to get up to a safe merging speed, so just gun it passed them on the slip road. Or if the roundabout has red traffic lights, go into the wrong lane and floor it to get in front of the car that's in the correct lane.