Roads seem busier far earlier in the morning - I have needed to get up almost 45mins earlier to just-to-say stay ahead of rush 'hour' where 3yrs ago I didn't need to.
Additionally, my route is fairly rural (single lane 60MPH NSL) with a fair few elderly drivers (stick to 30-40MPH everywhere), alongside HGVs and Agricultural vehicles.
All it usually takes is any two vehicles of those mentioned above to meet, and you have a tailback nearly a mile long as everyone is ground to a speed of 30-40MPH, due to the overtaking opportunities not allowing for more than 1 vehicle to be jumped safely.
'Safely' - many folk overtake on blind corners and over crests of hills, which I frankly cannot devolve myself to consider an option.
Additionally, the weather seems to provoke extremes in driving behaviour. Lower than 10'C prompts some people to drive and 40MPH maximum, then you get some absolute prat with something to prove who decides that 65MPH in a 60MPH isn't fast enough...