How interesting, I just read an article about the same topic from a 1985 issue of Analog! They had a couple of dozen different explanations for the Great Silence.

But it was optimistic. "We're only a few decades away from starships."

However, they did have one suggestion you might have missed, called "Water World".

The idea is that Earth is very dry for a wet planet, and most planets that have water might be completely water, so that nearly all intelligence would evolve in an environment that made technology more or less impossible.

I agree with your use of Occam's Razor here - the most likely hypothesis is that we are alone - but of course with so little evidence we can't do more than make educated guesses.