Earlier quoted context omitted.
Part of it is simply different television formats. The Office UK specifically aired on BBC One without commercials which meant that it had to be cut down to fit on a major network's timeslot of 20-24 min. Shows like that typically have to go to special TV stations like PBS or BBC America in order to get a commercial-free timeslot or (in BBC America's case) finagled into a less common time slot with weird commercial b…
The IT Crowd was actually aired on Channel 4, not the BBC. Channel 4 is publicly owned (for now…) but is fully funded through adverts. The ad break timings likely don’t match what you have in the US though (at the start and end and a single break in the middle over a 30 minute runtime).
NFL is an extreme example but I always found the comparison interesting.