Well guys as you may have heard there is a new Counter Strike coming out soon. And so as a marketing strategy the free open Beta named "Counter-Strike: Source Beta" gets a new update, and the update makes the game TOTALLY LAGGY AND SH***Y.
So of course they expect players of the open Beta to buy the new CS:GO because the Beta was actually worth playing.
Honestly I hate Valve and I think their business tactics are almost criminal, but that doesn't mean I won't still play CS:SB and eventually CS:GO.
It appears they have released another patch that fixes it.