Cruise control isn't as big a thing in the UK. We have bendy roads and drive manual cars not automatics.
Personally, I use cruise control very often, and the attention freed up by it I typically put toward maintaining lane position and checking my mirrors more often. It keeps the trips engaging and makes me a safer, more consistent driver.
I'm also convinced that traffic flow would be much better if people used cruise control more often. Speed variability seems to cause excessive lane changes as a driver inadvertently slows down and the cars following attempt to pass so that they don't have to slow down too.
I'll also say that by and large my experience in the UK is on most motorways traffic is sufficiently busy that cruise control is of relatively little use: there's enough variability in the speed of the traffic in front that you can't actually stay at a constant speed and there's enough traffic that you can't just pull out to overtake.
I don't know whether or not this is related to the use of cruise control, but I have observed many drivers using their brakes on the highway even when it's clearly not necessary. For example, they'll slow down behind a car before switching lanes instead of anticipating the traffic situation and either letting up on the accelerator before catching up to the vehicle in front of them or adjusting their speed and moving into the adjacent lane to pass.
Firstly, in the UK they aren't 'equal' lanes. They are for overtaking only. Undertaking is illegal. So we don't just change lanes willy-nilly. We change lane to overtake someone, and then change back.
Secondly, only motorways and dual-carriage ways are multi-lane. Most roads are single lane.