Not really what you're asking, but I've been thinking about films which were adapted for TV which didn't have enough material for a series, and which actually added something worthwhile.

Picnic at Hanging Rock didn't expand the story enough to justify a series.

The Purge season one wasn't justified, but season 2 was (exploring the days after Purge Night.

Scream worked as a series (at least season 1, haven't watched 2), letting the paranoia and suspicion build, getting attached to characters know they could be murdered).

Westworld works - there's so much to explore with the subject of Artificial Life, several seasons is warranted.

Anyways, these are just a few that cane to mind.