Is that really the case, though? The traditional peak hours were such that there were certain things which could be done, such as run trains quickly back against the flow as ECS, precisely match length according to expected demand (which was generally constant from one day/week to the next), and also carry out a load of maintenance between the peaks.
Leisure demand is both less consistent and less predictable, so you can end up with longer formations having to run across the board and be out longer, so suddenly a significant amount of your maintenance is concentrated on the overnight period. The latter introduces its own problem as you now need more depot space and resource.
If you look at something like how Great Northern used to be arranged before 2018. The bulk of the outer suburban fleets (317/321/365) outstabled overnight at Kings Lynn, Cambridge, Peterborough and Letchworth, which only a comparatively small number of units staying overnight at a proper depot - Hornsey. By contrast, the inner suburban fleet (313) stabled a lot of units at Hornsey overnight, with a lesser proportion outstabled at Welwyn, Hertford and Letchworth. This was actually quite efficient, though did start to break down as rhe 2010s went on as more and more 365s spent the midday running as 8-car formations.
Personally I suspect over time commuting will return as more employers come to realise that not all employees are knuckling down to home working. My neighbour is a case in point, there’s clearly not much work going on given how much time he now spends gardening or walking into town!