I'm fairly new to AirBnB but I believe it's because you chose a minimum price that AirBnB auto pricing recognize. So it can be higher but not lower. This is because the auto pricing only goes out for 3 or 4 months and your base price is reflected on all days beyond that. Look under Pricing -> Price Settings -> Base Price
Smart Pricing is on. If a guest wants to book more than 4 months from now, they’ll pay your base price, or the custom prices you’ve set.
Your base price is how much you’ll charge if Smart Pricing is off, or if other custom prices, like long-term prices, aren’t in effect.
Hope that helps.