But summary is:
1) Are you the people you are reaching out to “warm contacts”? By that I mean is there someone you know who knows them? If not you may want to try to start with people you already know.
2) What level of experience are you targeting for coffees? 1-2 yrs experience engineers? 5-10? 30-40 years? I have found that targeting people your own age yields worse results, but people just a little ahead of you in their career are more likely.
3) What kind of people? Some people are intimidated by going to coffee with someone new and some aren’t. If you can (and this is tricky) figure out who is more likely to say Yes.
So, people with already a well developed social capital are doing better of people without it. News at 11.
The point is that having this "social capital" is not neutral or random.
Personally, I find it really swarmy, but the purpose is legit -- talk to people that you don't have to talk to because you work or go to school with them.
For some people, doing the Silicon Valley coffee thing is a meaningful thing. It may not be for you. Maybe talking to an ex-coworker, reaching out to wish someone Happy Birthday on the phone, or something similar makes more sense to you.
I got my first consulting gig because a farmer I worked for as a middle schooler sent a vendor my way when I was in college. I'd drop by and say hello a couple of times a year when I was in the neighborhood. Humans are social creatures!