Working "as designed" (as a certain Maxoid would say). You don't get memories for everything, just things that the designers considered important enough, and I think there are plenty enough memories as it is.
Yea, but shouldn't the sims at least get the memory for the first woohoo? Otherwise, there's no point to sending Romance sims with the 'Woohoo 20 sims' LTW on vacation to bang random passers-by.