It does a great job of explaining it, Cain. You might not like the answer, but it's a clear and factual (as well as I know the facts, based on previous years of convention events) one. BattleTech runs more events because the events are shorter, some long events are counted as multiple events within the framework of how conventions designate an event, and BattleTech events can have one person overseeing multiple games, which is not possible with Shadowrun.
To build a bit more off Adam's answer and based on my two prior GenCons:
Grinders/BootCamps are literally one ongoing game of battletech. It never stops, so long as players are at the table. Because you're talking about a non-mission based scenario for a wargame (and they often use much simplified Introductory rules from the boxsets/Intro rules), you just have people show up, learn the basics of the game, slowly increasing the weight class of Mechs assigned. Rinse and repeat. No RP required, hence more time to play. There's the first point.
The "storyline" events have previously been broken up into two hour blocks. They tend to span six or more hours, but each two hour listing (while being the same battle/event overall) counts as its own listing. I'd imagine the Grinders mentioned above are listed the same way, in two hour blocks. Hence, it shows much more games available. Also, as Adam mentioned, there's no real RP here, hence no GM required for each table/game/demo. That means one ref can handle multiple small tables (or in the case of storyline events, one large table with 30 or more folks). Additionally, at the storyline events, you tend to have a much higher proliferation of BT vets, so rules are often handled amongst the very knowledgeable players, and GMs are needed only for rule conflict resolution. And not, you know, GMing an actual RP based Shadowrun session.
You're comparing apples and oranges (an RP game to a minis/wargame), with what sounds like the express purpose of showing lack of CGL support for Shadowrun. While that could potentially be the case, depending on your opinions of CGL, it isn't the case due to what you're suggesting. Meaning, simply because there are less SR games listed (which take more time, and a lot more intensive resources), that isn't the deciding fact on whether or not CGL is giving proper SR support at GenCon.