If serious, it's because double-you, double-you, double-you (6 syllables) vs world-wide-web (3 syllables). A syllable sort of represents the amount of time it takes to say something.
So it takes twice as long to say www.
If not serious, yes, it's because your German. But then again, German humor isn't really that.
It was a poor explanation. Double you has 3 syllables so it has nine all up vs 3. So it takes 3 times as long. I don’t think it was about the time but the ease of saying it. World Wide Web is a bit annoying to say
I’ve no better answer than “It just isn’t done.” Native English speakers at the very least would not interpret that as indicating the letter, they would interpret it as someone stuttering or what they’re trying to say is stuck on the tip of their tongue.