I also noticed that a significant fraction of drivers don't know how to use acceleration lanes; they wait at the beginning of the lane until they can pull directly into the main flow of traffic. Tailgating and weaving are probably so common because many drivers do not see left lanes as overtaking lanes, but rather seem to have a favourite lane that they always use; other drivers must navigate around them.
Also, the driving test in the UK takes about 1 hour, with 40 minutes of driving in all conditions (highway, urban, overtaking, merging, emergency stop, three-point turn, parallel parking in an actual parking space, etc.). For my American test, I had less than ten minutes of driving - I took a right out of the test center, drove for 1/2 mile, took a left then three rights and headed back to the test center, went round the back and parallel parked between bollards that had at least two parking spaces between them. That got me my license.
It's just a different culture here - driving is seen as a right, not a privilege.