The official reason is to reward their loyal fans, however as they are still in the relegation mix they probably want a big crowd to cheer them on as well. Perhaps they've seen how well we did in front of a big crowd against Dunfermline!
Saints quickly followed suit, instigating the same pricing policy as was in effect for the game against Dunfermline. This means it's £10 for adults and £2 for children, although adult tickets for the home end can be bought for just £5 by a season ticket holder. However, this only applies to tickets bought before 6pm on Friday 18 May - the day before the game. Otherwise you'll have to pay full whack.
With these excellent end of season bargains up for grabs, there is absolutely no excuse for any Saints fan not to go to the games and cheer on the team in their bid to avoid the drop.