I can't tell you how many people I know making very good money in tech and finance living in rent-controlled units paying ridiculously low rents in SF.
$900 per month for a one bedroom unit, with parking, in the Mission.
1000-1500 in a good area
I appreciate you telling us that you can't tell us (as much as everyone will appreciate this equally insightful comment).
lalala12399 is using an idiom in the American English language.
How? They must be illegal since those aren't longtime residents.
By being in the business before this tech boom. Finance has been a major part of the San Francisco economy since the Gold Rush of 1849 (one of the 4 US Mints is here, one of the 12 Federal Reserve banks is here, and a bunch of other banks have important offices), and techies have been getting rich and moving here since at least when HP was founded, in 1939.
Why, and does it matter? I have no idea how rent control works. Clearly it's a silly, broken idea, because, I, too, know people of people who have moved into rent-controlled units and benefited from it. Whether it's legal or not, well, who cares. It happens, and it points out why rent control is stupid.