Why do frames kill SEO?

I've often wondered just what is it about frames that throws the SE bots so. I assumed it was because once a bot followed a link in the nav document, the content document often doesn't contain links back to the main site, and so was a dead end for the bot. But suppose one DID include links, even invisible to the human eye, on the content pages? Would that alleviate the problem bots have with frames?