It is time consuming. Commercial hybrids are the result of years of developing special inbred breeding lines which are then used to develop the F1 hybrid. Of course a new op takes even longer to stabilize into a new variety. With an op the only way to recover the cost is to patent the variety (PVP). With a non patented OP, anyone can grow out the seeds and sell them. When op varieties were grown commercially, seed suppliers worked hard to maintain purity ( such seeds were sold as Certified) No longer the case. Most hybrid tomato seeds are produced in countrys with low labor cost.
http://203.64.245.61/web_crops.... In the days of Certified seed, isolation was the primary method of controlling cross pollination. Tomatoes are not prone to cross pollination except for a few types, but insects can accomplish the deed. One figure that is bandied about is 5 %. Note that most of the myriad of "heirlooms" came about from chance pollination more than those introduced by dedicated amateur breeders. Remember that a variety like Muletrain or Boxcar Willie may have given the breeder warm fuzzy feelings but no money.
