Getting the train is sadly not really a better option for some people.

In my case, I fly the LBA route quite a lot. It is often cheaper than the train, provides access to lounges which can cover dinner when I am on the late flight, and is convenient in my case as I live closer to LHR than Euston and closer to LBA then the train station.

It is also cost effective in terms of Avios, as I currently earn 1000 Avios per sector meaning I can book every 4.5th flight using Avios if required, even if this is for my travelling companion (I prefer not to use Avios for myself whenever possible as it makes more sense for me to take the paid fare and collect double Avios). This may all change when the new earning structure comes in making the benefit of Avios less rewarding, though the lounge is still a plus.