RSUs are frequently given during annual performance reviews to employees with good reviews. For my first annual review I received a score of "Exceeds" which is second from the highest. For that, I got 35 RSUs worth roughly $19K when they vest (at current price).
In theory, good employees will continue to receive stock grants that vest over time, thus creating incentives to both stay and to perform well.
I walked away with close to 100k on the table over the next 2 years because I couldn't stand the place anymore. Their golden handcuffs are awful.
The stock seemed like a mind-game to me, but it did work out to about 10% YoY increases in total compensation.
It's also inaccurate to characterize the stock as a one-time grant. The initial grant vests over four years (weighted on the last two years) typically you receive more grants after performance reviews, which vest over two years (again weighted on the second year.)
So in practice, you get a grant of 200 shares at signing, but by the end of year two only 50 have vested. At that point you have at least one performance grant, so you're probably getting shares vesting pretty regularly, at least four times a year.
Meaning the equivalent income to maintain your standard of living in Dallas is $81k, or ~70k less than San Francisco.