It's probably all they can do right now. It's really a risk reviving a franchise like Crash. Sure, the fanbase is there but it's another question when you find out how large that fan base is.And does it warrant another entry. Maybe if the Crash Skylander does well, they'll be a bit more persuaded to do a full game.
Skylander doesn't share any part of its demographic with Crash, so it makes no sense to check for demand for Crash through Skylanders.
They already have a great gauge for wether or not the Crash fanbase is there: The original Crash games released on PSN. They are constantly topping the European charts (like, almost continuosly, barring a few months where some random other games go on extreme sales), and the only reason they aren't topping the US charts is because they haven't been released on the PS4 as PS Classics, they're only available on the PS3 and Vita.