Spiggie beach with dog

OK, so can anyone explain to me how rail fares are worked out? I ask this as I sit on a train from Lancaster (which was disappointing) to Euston, in the first class accommodation with only me so far in the carriage for a mere £44.00.
I only booked it just over a week ago and the standard fare for the same journey was £58.00!
How does that work??

I'm`not complaining as I had a good time with plenty of tea, a couple of soft drinks, 2 double whiskeys and 2 snacks on the way...
I just hope that the general public don't discover this great way to travel the country and therefore leave more seats open for me!