What's up with the hyphen in "orang-utan"?

According to the Wikipedia page about orangutan, that's the Malay spelling (although it looks like it is actually two words):

The word "orangutan" comes from the Malay words "orang" (man) and "(h)utan" (forest).

Perhaps this phenomenon should have a name, maybe "hyphen decay". A noun phrase becomes so current that starts being treated as a single word and is granted a hyphen in recognition of its new status. If the word becomes popular enough, even the hyphen is dropped and the words fuse.

"Bell boy" becomes "bell-boy", then "bellboy". Ditto for hundreds of other words from "type writer" to "lap top".

Orangutan is unusual in that the words originated in a non-Western language (albeit one that used Latin characters) and the hyphen was apparently added in the process of importing the word into English.