I can think of several scenarios that could create this situation. Your Realtor may know that several other buyers have viewed the property recently. He or she may know that other offers have been received. They may know (or have recently learned) the price of a bid the bank or seller has rejected.
Start with your Realtor. If you can't get an answer you can understand (even if you don't agree with it) you might want to consider a different Realtor