I think the “Valley” is just sufficiently expensive and/or newly settled that the probability a person would be a net negative to introduce was low enough that there did not need to be as much gatekeeping as there is in the east.

If you were knowledgeable enough to move to the Valley, if you had the wealth and connections to move to the Valley, then you already passed some of the checks needed to be someone who would be a sufficiently good bet to introduce.

It might already be the case that the Valley has changed to be more similar to the East.