Basically the sellers end up bidding for the opportunity to sell. So basically some sellers won't be willing to sell below 89, more won't be willing to sell below 88, and even more won't be willing to sell be 87. And it works the other way too, so the lower the price gets, the more people are willing to buy. So theoretically, when the number of buyers equals the number of sellers, transactions end up occurring. This is assuming that the market is efficient, which isn't always the case.
If there were 1000 sellers, the price would drop even lower, because there is more competition among the sellers.