Note that I work for HashiCorp so I have a clear bias. I tend to shy away from these comments because of that but there is a certain addition I'd like to add here. The other comments around this are good so I won't talk about those.

The surface area of Vault capabilities is much larger than EC2 parameter store and through the lens of our paying customers, most are using Vault for many more of the backends (the most popular probably being PKI).

For pure AWS-based companies, parameter store could provide a fine solution for basic key/value secrets! I don't want to bash at all, I just wanted to make sure for any readers that they don't mistake Vault for purely encrypted K/V.