Think it's a case of cash availability. I know I used to be a bit more wary about using trains as they can be quite expensive (especially when compared to Megabus), but these days I'm more inclined to use the train when I can afford to do so.

Especially in the summer months though, I treated £20 as two Megabus Wednesday trips or one weekend train trip... In my eyes, two trips was better than one, if £20 was all I could afford to spend on travelling elsewhere in the UK for a trip that fortnight/month.