Native plants are obviously happy with local climates and soils. Otherwise, they would not be native. They had been living here long before the first landscapes. They survived without irrigation, fertilizer or any maintenance. Regional varieties adapted to regional environmental conditions. Some of such varieties became cultivars that are now familiar.
A variety is, more or less, a naturally occurring variant. Unnatural selection and breeding produced some varieties. Generally, varieties are genetically stable enough to replicate for at least a few generations. A cultivar is a cultivated variety. It is unable to replicate by natural processes, so propagates by cloning. All clones are genetically identical copies.
Most cultivars grow from cuttings. Some cultivars of exotic (nonnative) plants are grafts. (Not many natives are conducive to grafting.) Regardless of technique, propagation of all cultivars is vegetative (without seed). Seed of some cultivars can produce plants that are similar to the parents, but not indistinguishable. Some will likely be completely different.
Honestly, most native plants are not as appealing in home gardens as their cultivars are. Some are desert or chaparral plants, which can get scraggly through summer. Some are sparsely foliated with irregular branch structure. Like the majority of exotic plants, several native plants benefited from some degree of refinement. It is a fair aesthetic compromise.
This is partly why landscapes of native plants look nothing like forests or unlandscaped areas. The dense and strictly conical form of ‘Soquel’ redwood is very different from that of wild trees. ‘Carmel Creeper’ ceanothus is greener and more densely foliated than wild counterparts. ‘Ken Taylor’ flannel bush is likewise unnaturally dense, low and mounding.
The other primary reason that landscapes of native plants are so different from the wild is that they typically include species from other regions. Some of the penstemons that are popular as native plants throughout California are actually only native to the Siskiyous. Limiting landscapes to true regional natives would produce very different results.