1. Because the German ones list to starboard (it leans over to the right)
2. It's cheaper than the Spanish ships.
3. It would enrich the Military Industrial Complex (to use the terminology of a Republican president) by costing billions to design one from scratch that probably wouldn't be any better than the plans they could buy from the Italians.
The Italians would have to build it in an American shipyard.
The two 'not from scratch' American versions are based on the two variants of the LCS which have proved themselves unsuitable for any role in which they've been tried, and lack endurance, firepower, and reliability. (The current LCS boats (I wouldn't call them ships) should be passed to the Coast Guard, which might be able to find a use for them despite their limited range and firepower. Coast Guard probably doesn't want them, however.
Huntington Ingalls Industries might beg to differ (this press release from a few years back):
HII has done a low-key pitch for a larger version of the National Security Cutter for the USN frigate competition.