I guess they ran out of episodes. I do agree though - it's bad enough that daytime fodder has creeped into the old Grandstand slots, never mind being on the edge of Saturday night primetime, which for both the BBC and ITV used to begin before 6pm.
The BBC haven't aired films on Saturday nights regularly for a long time but I do think there is other content that could get an airing there. For example I think it's a real shame that Peaky Blinders picked up many fans on a second airing through Netflix rather than the BBC, when actually I think the pre-MOTD slot is ideal to give shows such as that, and the likes of Line of Duty and Luther, a repeat run - dramas that have really picked up an audience over later years but viewers didn't necessarily watch from the start.
Arguably too as repetitive and unimaginative as they were the BBC needed the lottery shows as much as the lottery needed the BBC.
I preferred the internet when it had a sense of humour.