My company is a small business but we require Okta SSO for every app. What is the reasoning behind SSO being an enterprise feature (aside from the fact that most SaaS apps do that)?

This is a blocker to us using many SaaS products because the enterprise tier is always very expensive. I think TeamRetro got it right with SAML support at the first paid tier, we started with a smaller plan and stepped it up as we grew.

So, perhaps you might consider providing SCIM support at the enterprise tier and SAML support at the business tier? I feel this is a nice compromise between security and administration hassle.

The simple reason is that it requires setup on our side. Do you see SSO as a blocker to trying? What we've seen teams do in most cases is use the free tier with email signup and try it out for a bit, once they like it and want to upgrade they contact us to upgrade and set up SSO.