I wouldn't say they're making an ant-man movie just because they want to. It's been in development for a long time.
Word. I'm pretty sure it was one of the first projects in development, but then production was a mess. That guy was working on it - it got nowhere, then backed out - and then they had problems finding someone else on board or something to that affect. I'm pretty sure dude who finally got the job to direct Ant Man was like fourth choice
I'm pretty sure if everything had gone right, Antman would've been one of the first movies released.
It just didn't happen that way. In the end, it all worked out.