What is the plausible reason for availability of most of the tomato varieties in the market to be almost uniformly oval shaped and firm

Reduction in genetic diversity is the plausible reason for the availability of most of the tomato varieties in the market to be almost uniformly oval-shaped and firm.
Inbreeding, genetic drift, restricted gene flow, and small population size all contribute to a reduction in genetic diversity. Fragmented and threatened populations are typically exposed to these conditions, which is likely to increase their risk of extinction.
An available variety of tomatoes with an oval shape and firm is a hybrid variety which ultimately leads to the reduction in genetic diversity.