Perhaps because lego is one of the best things about childhood - the toy that spans gender and age and lasts forever (except those bits your little brother chewed on, they are never going to click down properly again. It was just the bit you needed too!).
So combine lego and movies and - cuuuuuuuute!
Thor! Logan! (which, incidentally was on TV last week (Origins) and I had to stay up and watch it again).
And for once, not Comic-Con exclusives. LEGO acquired Marvel and DC licences and hopefully soon we can see these babies fo'real.