[thanatropism]

Isn't this because it's so different from anything else?

You can sort of divine some German if you're an English speaker and some Italian if you also understand Spanish, etc. But hey, Japanese is highly regular and also very hard to learn.

(I did play with Duolingo Hungarian for a while, and it seems interestingly regular, although not in ways you might expect)

[throwaway7645]

Only partly...it has lots of suffixes and prefixes for pretty much everything too. They says it's nearly impossible for a foreigner to learn (of course not true).

[hanasu]

Mostly because it's extremely agglutinative.