I think it's because the U.S. overall seems to prefer B&M. I'd think a smaller park could end up with one pretty soon and they'll end up in other places as well, like eurofighters (though we don't have many of those either). I could see one at Mount Olympus or Holiday World sometime (no time soon though). Both parks lack a steel coaster not counting kiddies. If Kentucky Kingdom ever reopened a mega lite would be the "big coaster" Ed Hart says he will build. It seems like in the US smaller parks wanting a good coaster build woodies because they tend to be cheap, but that could change pretty soon.
-A Mega-Lite is a bad choice for major parks as the capacity isn't high enough (theoretical is only 800 riders per hour) and it doesn't look too impressive compared to larger rides.
-A small park cannot afford the price tag of the rides, as they are still probably a $10 million investment.
-Many of the medium sized parks where the ride would be a good fit already have a similar ride and/or aren't interested in a major steel coaster.
-In the US, the general public seems to be addicted to record breakers and inversions, neither of which are featured on a Mega-Lite. At the same time, many people shy away from ejector airtime, which is the primary component of these rides, as they feel it is a design flaw and makes the ride unsafe.
-US parks, especially the corporate ones, tend to modify their attractions so that the intensity level is more appropriate for a wide audience by adding trims on the coasters, thereby taming the ride and reducing forces experienced, thus defeating the purpose of an airtime machine.
-Intamin AG is known to have significant reliability problems with their designs and has the most restrictive restraint systems of the major coaster manufacturers.
-There are only a handful of parks in the US I can think of where a Mega-Lite would actually be a good fit, including:
California's Great America
Knoebels Amusement Park & Resort (if they want a major steel coaster)
Mt. Olympus Water & Theme Park (if they want a major steel coaster)
Six Flags Discovery Kingdom
Six Flags Kentucky Kingdom (if it reopens)
and possibly one or two others.
Knotts (if miraculously they can fit something in there)
For 2013 people thought they'd get a giga. Ha!
SeaWorld Orlando- this wouldn't happen for years but it would be a good 3rd major coaster.
Silverwood Theme Park- They've surprised me with their collection of rejects from other parks and they're becoming a big ticket place. Maybe in 5 to 10 years they could have enough money for one.
Valleyfair- In the last few years Cedar Fair (and Six Flags) have FORGOTTEN their smaller parks. Show them some love! A mega lite would fit right in there.
Kings Island- maybe not a mega lite, but if they don't use the Son of Beast space on ONE coaster and instead multiple rides a eurofighter or el loco would fit right in at the Action Zone area. I think Flight Deck is a goner too so Kings Island has a lot of space available in the next 5 years or so.
Maybe my choices could be a little ridiculous (especially Seaworld) but hey, you never know.