Tebow has a better playoff record in Denver than Manning does...
Lot's of mediocre players have a good run, it doesn't mean they aren't still mediocre players.
Denver knew Tebow wasn't the answer at QB even while he was on his winning streak. His mechanic's are terrible and he isn't the kind of player a team can build a franchise around. It's as simple as that. Tebow is a good guy and a winning personality, but he isn't likely to ever be a starting QB in the NFL. If he could be truly happy with a backup/utility role, someone might sign him.