I think it is to easy to blame issues like Sunday working on the Dft/Government but GWR▸ (Great Western Railway)/FGW▸ (First Great Western)/ASLEF» (Associated Society of Locomotive Engineers and Firemen - about)/RMT▸ (National Union of Rail, Maritime & Transport Workers) have had 26 years to sort this out and the DFT▸ (Department for Transport)/Government haven't been micro managing them the whole time.
In my opinion it is a failure of both the management and employees to come to an agreement about this issue and neither appear to care about how this may impact the travelling public.
And I am not sure why those who advocate (like many on this site) for either people to travel by rail or for further investment in rail bother when many of those running the railway seem to think that the world revolves around them and have forgetten that the passengers (and taxpayers) need a reliable 7-day service.