It's probably a weird oversight, since they decided to give away the PS3 ver in this special case. I have no problem if them doing something awesome and out of the ordinary causes some technical hiccup.
But anyway, too late for you this month, but on the mobile site, there's a category if you scroll down for PS+, then there's a category for 'Free Games'. That just has all the free stuff in 1 list that you can add to cart-> continue shopping -> add to cart -> etc. Both Dragon's Crowns were in that list. I'm not sure how you were getting to the games but this list will probably work better for you in the future.

