There are many theories and little evidence of how snake reproduction and reptile hormone cycling happens:
I think the most accepted theory on brumation is that a long cooling period following by a gradual warm-up initiates a physiological response and production/release of hormones that stimulate egg and sperm production.
Most breeders have found that while successful breeding can occur without the "winter-like" cool down period, numbers and success of offsping seem to be better with.
I have my own personal thoughts of why breeding without brumation happens but I haven't had a chance to scientifically prove my hypothesis.
Good luck