Last quarter, they made $10.12 per user[1, slide 4], however that's not evenly distributed. They made $53.01 per user in US and Canada. But even that isn't evenly distributed. The users who are likely to pay for the subscription are also the most valuable to advertisers because they have disposable income. Some Instagram users see ads for luxury cars, real estate, and vacations, while other users see ads for dollar stores and dropshipped junk. FB earns much more in their auction from that first set of users, but those will be the first users willing to pay to opt out of ads.

Dynamic pricing would probably offend both audiences - "what do you mean the algorithm thinks I'm worthless?" "what do you mean that I'm worth thousands of dollars to you?"

[1] https://s21.q4cdn.com/399680738/files/doc_financials/2021/q2...