It's because most of them suck, unfortunately. Tampa just hasn't drafted very well at all.
Ultimately, Tampa won't be a deep-playoff team until they get more experience and continuity. They have no savvy vets on their squad who know what it takes to win. And it's not like they're Seattle where they just have to much talent (that fits in their scheme) that they can overcome their inexperience. On that subject, the Bucs need more talent, especially in their depth. That comes from drafting well. I'm not sure they had that great of a draft this season, considering they took a running-back in the third when it wasn't a position of value at all. They'll need to stack on a few years of good drafts and solid signings to get better.
The Bucs need to focus on becoming a good team before they think about how many playoff games they want to win. A lot of teams win it all by peaking at the right time after looking pedestrian going into the tournament. I actually think the 2010 team would have won a playoff game had they not been screwed by the refs. They lacked talent, but Freeman was special that year. Would have been interesting to see them try, especially because Tampa getting the right call would have knocked the Champion Packers out of their sixth seed.