Think quickly about your favorite sport. I'm sure you can easily think of one team that is a perpetual basement dweller. For example, the Tampa Bay (Devil) Rays are constantly in the bottom of the league (MLB). I was a bit surprised to see their current record standing at 17-15.
Some may say that it's up to the owners and general managers to provide their cities with competitive teams. If they were good businessmen and cared about their team and their sport, they would do what it takes to create a successful and profitable team.
I'm almost of the mind that it has more to do with the size of the leagues. The NFL has the most teams (32). They're probably best able to support their teams, all in the US, due to the way the American public devours that sport. Many people live, eat, and breathe football. The one thing I think that supports that sport is the length of the season, being just four months for the regular season, the playoffs taking another month. Because watchers have to wait more than half the year for the next game, excitement really builds up over that time.
All the other major leagues (NBA, MLB, and NHL) all have 30 teams each. Baseball probably is the next most popular sport, though its interest is waning in fringe fans. Issues with steroids and other drugs as well as the lack of respect, for lack of a better term, for records have dulled the sport's image. Baseball is very much a numbers game. People recognize the numbers 755, 61, 40/40, etc. without much thought. But it has its fair share of terrible teams. Colorado had a couple good seasons, and now, for the most part, it's a pretty mediocre team. The Washington Nationals (formerly the Montreal Expos) are starting quite blandly once again, even with the brand new stadium they're playing in.
I don't follow basketball hardly at all, so any comment about them may be mere speculation on my part, but when was the last time the Clippers had a decent season? I remember thinking in the mid 90's that that team was a constant bottom place team.
The NHL is the sport I follow most. I really get into the excitement of it all, and now that my beloved Penguins are flying through the playoffs, I'm loving every minute of it. But, there are a few teams that could do with a better team. The St. Louis Blues have been pretty bad for a while, even though about fifteen years ago they were a decent team. I always thought of the Islanders as being a pretty lousy team, though at times they do show some flashes of inspiration. And for a league that glorifies its history of the "Original 6", the league sure did expand extremely quickly
Over four major sports, there are 122 teams across the continental 48 states and southern Canada. I think the NFL would do fine as they are. I don't know about how well the NBA's teams are doing, so I can't guess what would be a decent solution for them. The MLB and NHL probably would do fine, if not better, if they reduced their size down to about 24 teams or so. Better talent per team, better support per team by the fans, less travel, better rivalries, and hopefully fewer perpetually terrible teams.
But I'm no commissioner.