- Chef and Puppet are too expensive for most companies to acquire, and have too much operational cost for too little revenue
- Ansible got a strong following in the SMB space, Red Hat probably thinks they can move that upmarket some
- Ansible's agentless configuration management has potentially strong applicability in a container world (why do I need a chunky agent to configure resources on my docker image? What if, for some reason, I need to affect change on running docker images? - I realize this is a bit of an anti-pattern for docker, but it was something I heard a lot from big enterprises)
$100m still sounds very high, kudos to the ansible folks who have come a long way in the last few years.
EDIT: one more piece I didn't think of here - the openstack side of things is an area where Red Hat has made big long-term bets for the future of the company, and it probably helps to justify the price in terms of backstopping their openstack support.