It's also harder to continually sell iterative products to the casual audience. Making one f2p Professor Layton app on iOS/Android and then doing constant updates to it would have made a lot of sense. There's probably actually still a market for it given it's been a while since most of their audience even realized that a new Professor Layton game came out.
Although I do think it'd be difficult to monetise it. Buy hints for the puzzles with real money? Get one chapter free and buy the rest? I don't know how I'd go about doing it myself to be honest.