Could be the age of your site, but remember, TF is a Majestic metric, and there is no reason to believe that it alone determines Google's rankings (if for no other reason than Google didn't come up with it). Like any other metric, TF can be manipulated, and if any of Google's zoo-ful of algo updates is made to catch on to what you're doing, you'll be slapped with no chance to rank.
Just like investing, think about *diversity* in how you assess your linkbuilding. And always do a manual review of your own backlinking efforts. After all, you wouldn't buy a stock just because of some metric, right? You'd want to dig into their business plan, etc. Same general idea.