This has happened across multiple TOCs this year (SWR have already done it, Southern have done it recently) - the official position seems to be that advances on morning peak journeys were a short term measure during covid and passenger numbers are such that they shouldn't be able to continue (and bluntly, as someone who is affected by this, they're right)
The only way of 'getting around it' is to either book further in advance and hopefully there is at least some availability, travel at a later time or reduce the number of days you travel.
The only way of 'getting around it' is to either book further in advance and hopefully there is at least some availability, travel at a later time or reduce the number of days you travel.