Traditional breeding takes half the genes from one plant and half from another to produce a new plant. To get a rare trait, such as resistance to a new virus, breeders may not have much choice of the source. So often, using conventional breeding, they have to take a lot of not very useful genes into the new plant to get the one they really need. Then a lot of time is spent breeding back into good plants to get rid of the junk genes.
Sometimes. to get a really rare gene, plant breeders have to go to a related species that is not commercial and find a way to get the gene into the commercial species and commercial cultivars. If they do not use biotechnology, then they have to get lucky and build a new plant that is the vegetable world's analog to a mule. People have domesticated the major food plants over thousands of years, and the cultivars used by farmers have been cleaned in that time of genes dangerous to man. The species from which important new genes are found haven't gone through that process, and often harbor dangerous genes. In any case, the tests used for the products of biotechnology are not used for the products of traditional breeding.
Properly don't, biotechnology not only produces needed new cultivars more rapidly, but also of more proven safety.
(I was the project officer for a major conference on biotechnology applications for developing countries in the early 1980s, and worked for the following 15 years managing a program funding biotechnology research and development projects, serving for part of that time as the officer responsible for assuring that the research was demonstrably safe.)