Later, when I designed the logo (the curvy LÖVE text), I added the umlauts on a whim since I decided that something was missing from the logo. That's how it became LÖVE. I also added a sarcastic copyright symbol to the logo, although that is removed now.
Source
You can also see on the homepage that there is no ® in the logo. Only on the wiki, but probably because no one bothered to change it.