Just curious [moved from San Francisco Bay Area board]
Probably a dumb question but, why do some popular/busy restaurants NOT take reservations?
Fairly simple answer, actually. They don't have to. When people fail to show up for a reservation, it costs the restaurant money. In fact just managing reservations in general costs money. So until they're not 100% full almost every night at the peak dinner hours, they're probably not going to take reservations.