Not iTunes, the rights holders. iTunes is a store front for other companies which sell their movies, tv shows, music, etc through the iTunes Store. If they decide not to sell them through iTunes any more it’s not Apples decision.
If you want to keep access to the things you’ve bought on iTunes make sure you download a copy locally.
This has been going on ever since they sold movies, unfortunately. Studios end their license deals and refuse to renew and the movies get pulled.
This is one reason to download your movies instead of relying on the convenience of Apple storing them in the cloud for you. Once a movie is on your drive it won’t be deleted.
While this is an accurate story, it’s merely an old one refreshed by one of the content-$kimmers over at Forbes. I read this Reddit post the other day, but it takes a Forbesian writer to refresh it into a breathless bit of clickbait. 
Follow-up: that guy moved to a different country, lost access to movies he purchased in 1st one, and region-change is a known issue for re-downloads.