LDAP works really well until you have either too many users, or too many endpoints. Then it doesn't work at all. There's no (cost effective) way to get past all of the replication traffic flying all over the place. Eventually consistent models are awful for things like ssh keys and passwords that's exacerbated significantly when you add caching to the mix to ease the load on your ldap cluster.

Adding extra brittle moving parts like LDAP and linux clustering to a greenfield deployment just doesn't seem attractive when a CA is so easy to run, and you should already have one if you're doing config management sanely.