Germany is Europe's largest economy and one of its most active Bitcoin markets, with BaFin-licensed custody and a growing range of regulated Bitcoin products. The .de TLD signals "this is for the German market" — essential for any Bitcoin product serving German-speaking customers. German-language naming is still far less crowded than its English-language equivalents.
.de is the largest country extension in Europe and the default trust signal for German customers. A German buyer landing on a .de assumes local jurisdiction, local support and local liability — assumptions a generic extension has to earn instead.
For a Bitcoin business that matters twice over: the product is unfamiliar to most of the market, and the extension removes one layer of unfamiliarity before the page has finished loading.