I get maybe 50 or so tomato plants in about 1 square meter in my garden, just from the seeds that are left in the ground from last year's tomatoes. (Of course I don't let all 50 grow and instead give most away.)
Those are not going to bear impressive fruit. People who grow tomatoes for sale almost exclusively plant hybrids. Making hybrid seeds is even more involved, and they cost more, but the crop is much larger, so it’s worth the hassle.
