You must understand the difference between hybrids and species. Species must produce seed to multiply. They grow in the wild and usually come fairly true to the colony of plants they are a part of in the wild.

Hybrids are a cross between two different plants. Either one may be a species or a hybrid. The seed produced on hybrid plants is not true to the parent plant or the hybrid plant my not produce seed. Sometimes the seed is not viable or produces a totally undesirable plant. Sometimes it produces a plant superior to either parent.

Species are propagated from seed, but special forms are propagated vegetatively, usually from cuttings.

Hybrids are propagated from cuttings.

Special crosses are made and the seed collected and sown and tested to see if it produces any desirable plants.

Here is a link that might be useful: Propagating Azaleas