Another one of those problems every company seems to try to solve on their own. :P
I totally agree (we did), though Confidant is in some ways trying to be an extension of existing AWS tools. I'm curious what you're using though since I've felt for a while now that every one of these secrets stores have faults or are a giant pain to work with. Confidant may be the least offender in that regard & anyone that is trying to make being secure easier or trying to make better tools gets an A in my book.
My company is using Vault as far as I know. I think HashiCorp is doing a decent job identifying the sort of things every company is trying to reinvent