The changes in the U.K. appear to have been made piecemeal over time. It started in 1997 and they finally made some changes in 2005, when it was recommended that the House study sitting times. The changes were finally made in 2012. They eliminated Friday sittings between 2012 and 2015
I emailed them to find out more about it, because it must have happened so recently that I couldn't find any information on it. But they did it piecemeal. In the U.K., the House sittings began later and ended later, and they gradually moved them all to earlier.
In Australia and New Zealand, their procedural manuals—their equivalent of O'Brien and Bosc—make it sound like they've sat like that since the beginning. It might not be the most useful comparison because Australia for half of its existence has had three days a week. From 1950 to 1984 it sat three days a week and more recently it sits four days a week. New Zealand only sits three days a week and it made it sound like that's always been the case.
I looked to see if anything said why they didn't sit five days a week and I couldn't find any information on it. It might be something worth asking officials from their jurisdictions.