Why would the price inflate? Is it out of print now?
Perhaps not, but being released more than 7 years ago, many would assume that it is out of print now. But I can tell at least through Amazon U.S. that Amazon U.S itself (not an associated vendor) still has brand new Alien Legendary Encounters stock to sell, and so does Upper Deck itself, i.e. it has yet to sell out, so no price inflation.
On the other hand, Predator Legendary Encounters appears to have sold out and now it's all about supply versus demand in the secondary market. If there are more consumers that want to buy your product than there is product, it drives the price up. And the Predator version went way up.
Perhaps Upper Deck overestimated demand during their manufacturing run for Alien and/or underestimated demand for their manufacturing run for Predator? Who knows, but that's the current state of things.