We know matches a political narrative (anti-liberal, anti-tax) and that the right, such as on Fox News, has long pushed it about CA. That would explain why you hear it so much.
EDIT: I'm trying to avoid discussing the politics of it on HN, but ignoring the narrative is like (as I said elsewhere) ignoring the Sun as we talk about Earth's orbit. It's impossible to discuss it seriously or honestly.
Based on what? Lots of people repeating something - we of the Internet age know better than our predecessors - isn't evidence of anything but 'viral' narrative, and raises no real question other than 'where did it come from?'
Anecdotal data you collect yourself is subject to your own biases, but is probably a decent reflection of the bubble you live in.
Tech workers who can work remotely night be more likely to leave but make up a small part of the population of the entire state.
I also wonder if every cohort in SF/SV goes through a pattern where many people they worked with leave the area as they get older. So many people I've worked with there left over the last ~5 years as their lifes changed in things other than tech became important. In many cases this move was somewhat involuntary and driven by high cost of housing and other necessities like day care. So there always might be people who feel like everyone is leaving.
We are hearing a ton of these anecdotal stories very recently about Californians moving to other states, especially wealthy, higher income individuals. My gut feeling is that there is some material shift behind it and our systematically measured data could simply just be lagging at the moment, or they are measuring the wrong things.