Business Model | Maintenance Plan

I’m curious how web designers offset the monthly maintenance plan - assuming they’re offering one with their past/current WP builds.

If the average maintenance plan is $100, then thousands is being lost each month as there’s no plug-ins, updates, hosting… anything.

Don’t get me wrong, I love the product - just trying to understand how people are translating that into a business with reoccurring revenue?

Thanks!