Wow! First, let me say that NO convention is like SDCC. I look forward to it every year and hope it stays in San Diego, especially if the city decided to expand the convention to meet the monstrous demand.
Los Angeles has no conventions? Really? Granted we don't have SDCC and none equal its scope, but we have a variety of shows every year. The Los Angeles Science Fiction and Comic Book convention has run monthly for decades, first at the old Ambassador Hotel (which I'm old enough to have attended) and now at the Shrine Auditorium. The E3 is held here each year. Bot Con is here just about every other year (how many of those have been in San Diego, Tycho ?). The best of all the Star Wars Celebrations, IV, was here (anything in San Diego?). Wizard World has shows here on annual basis, as does the Disney D23. And there are probably shows I've neglected mentioning.
Wonder Con is owned and operated by Comic Con International. It is usually held in San Francisco, but due to renovations at its usual facility, the show was moved down to Anaheim. I suspect, purely speculation on my part, that CCI is going to gauge the viability of this venue for potentially staging their annual INTERNATIONAL comic con there. From what I understand, the City of San Diego and CCI are butting heads a bit about the expansion of their convention center. CCI might be holding the show in Anaheim just to leverage their position a bit about moving the show elsewhere. Who knows for sure, but I annually plan my summer around a July weekend in San Diego.
I truly hope that Comic Con stays in San Diego, that great suburb of Los Angeles.