3. The seeds had to spread
Seeds don’t do you much good unless farmers are willing to plant them. There are well over 1,000 hops farms in Hallertau, most of them surprisingly small -- 33 acres on average, whereas the average farm in Yakima, Washington is 450 acres. All the farms buy from the same source, but they’re not obligated to buy any particular seeds.
That means a lot of individual farms, many of them operated by the same families for generations, had to decide, “Okay, we’ve been planting traditional German hops with peerless agricultural expertise since time immemorial, but I’m willing to take a chance on these crazy newfangled cultivars.” There probably isn’t a direct German translation of “newfangled,” but you get the idea.