I had the same experience some years ago, as did everyone in line with me. No other car rental company in FRA requires that you buy their LDW, which is why people are surprised. Yes, it's in their T&Cs, but so what? It's a calculated ripoff because nobody else does that and that way they catch everyone off guard.
They apparently don't need any repeat business because as long as their practices aren't well known, they'll keep drawing in suckers.
If anyone from Dollar/Thrifty is reading this, please know that I have assiduously avoided renting from you even in the US, even if it costs me more, because of my experience with your FRA licensee.