A first year hop plant (or any other perenial plant) wants to flower and set seed. This is what plants do. If you remove the cones/flowers before they set seed it diverts its energy into producing a stronger rhizome/root for next year. Yes, you will get a harvest from a first year plant, but if you remove the cones, before they set seed, you will get a much bigger crop in the following years.
Its the same for all perenial plants.