I'm pretty sure the bots are farming "Drops" which they'll sell for money. Every week you get a free case (or skin I think) which the bots are taking advantage of
Anyway, GP's is not my impression of 1.6 back in the day: lots of bot servers back then too.
There is decent money in it. Back in CSGO I had a VM running two full bot servers at a run cost of ~$3.xx per week to earn ~$30 fully automated.
From Valve viewpoint this might even be preferable as alternative is users actually downloading those games and just running them. Not to mention the 10%-33% tax they take on their market trasnactions.