Slow vs fast bus drivers

I was taking a picture of the buses but 
suddenly a person in this pink panther 
suit started crossing the street! ^_^

A topic between two men on the bus recently caught my attention which was about why there are slow bus drivers and why there are fast bus drivers. That really amused me for a few minutes, because I wonder at the same thing everyday! Sometimes I get to work really early and sometimes not.
With this kind of thing happening at certain times of the year (or maybe every day) is it because of school holidays or is it the time of the season, or could it even be because the bus driver is either early or late with their schedule and have a fear of those monitoring them will get a shouting at... Who knows!
I like fast bus drivers although there are times when I want them to go slow so I can read whatever I'm reading on the bus. But I hate slow bus drivers, especially when there happens to be no traffic at all and I'm trying to get somewhere on time!! And I especially hate it when the bus drivers are late and you've been waiting (probably for more than 15 minutes) for a bus, more than one come at the same time. Irritating for a lot of people :p
Getting on the bus is probably one of the cheapest methods of public transportation (but not that cheap in London because of the annual rise in fares - not really fair on the London tax payee)!
But the best thing about being on a slow bus is that you can see a lot of things in London whereas on a fast bus, you will only get the smallest glimpses of everything...

This is what I got to see whilst being on a semi-slow bus...

Protesters in London!