Certified GKH Gardening Expert
I'd say the local stores only carry the most popular seed varieties whereas the catalogs carry more selection plus hard to find seeds. If you aren't looking for any specialty items then the local stores probably will have what you want.
I think there is a convenience factor too with the catalogs and they run sales, too. Catalogs also offer a chance to sit and peruse the varieties and decide at your leisure what to buy.
I have not noticed any difference in the germination rates between the catalogs and the local stores. I've had seeds not come up purchased from catalogs as well as locally bought.
This article might be helpful:
https://www.gardeningknowhow.com/garden-how-to/shop/tips-for-ordering-plants.htm