I have a Facebook page with almost 15k natural likes. Every time I post to that page, the reach only ranges from 900 - 1,500. That's roughly 10% of my "fans". Is this the expected behavior, that Facebook just shows my posts to 10% of my fans? I guess they're doing this to force me to "Boost" my posts?
Yes, Facebook does this to promote their marketing service. If post reach is low, there is a high chance of getting more page promoting advertisements, so facebook does this.