Directors cuts started to become more common when home video took off.

Movies that were initially cut in length for theatrical release or butchered by the studio were given a special re-release with those scenes restored.

But it wasnt standard practise and was only really reserved for a very select few movies.

Until they realised that people were buying all these different versions of the movie and the industry has never looked back since.

Now it seems some directors and studios purposefully make films with a mind to do a directors cut, r-rated or special version on bluray later on.

Some directors do it was a valid reason. With Peter Jackson and the LOTR special editions which were far too long for cinema release and the extra material did make the movies better.

But other times they just release an "unrated" or "uncensored" version and add some tits or language. I cant remember which one but a film that was re-released as an "uncensored" version in the uk wasnt cut in the first place.