The five referees sitting behind me in the stand during the one game that only had one referee told me it was a volunteer based thing, and they didn't have to do the line. Personally, in a crucial last game of the round one team is out the other is in match, you'd hope for more but oh well.
In saying that, a linesman might have spotted the goalkeeper picking up the ball, dribbling it to the edge of the box, then picking it up again! I spoke to the referee about it after the game and he said he gave him the benefit of the doubt the first time... Still did nothing either time tho.
Anyways, I am not blaming that or bitter about it. Just random that's all.