The only people who care about SSO are large enterprises. Coincidentally, large enterprises also are the only customers that make SAAS profitable. Every other plan is part of the sales funnel to the big enterprise contracts.
I run a bunch of services for friends and family, things like Immich, wallabag, mealie etc. Less than 10 users, but do you expect me to crate and maintain separate accounts for each one for every service?
The SSO tax is stupid. If your whole business model is based on putting SSO behind a paywall, it’s a sign of a broken business model.