Parasyte anime 20 years after the manga finished - Why? My question is Why?

Most manga that have anime adaptions get them while they are still on-going (even if the manga ends during the initial anime run.)

Can anyone give/think of a reason why they suddenly made this after 20 years?

Edit: Glad they did though, its might be my favourite anime.
Because they felt like it. Simple as that. Though the Parasyte Live action movies have been in development hell for years, so the anime might have simply been a marketing tool to get people interested in the movies since the Manga is pretty old, and even the reprint edition (from 2006 or so) can be kind of hard to find.