Why is the Dallas Mavericks team so old? They also have low draft picks. So they won't stand a chance!?

In the near future that is. They may still be good next season, but I don't really understand how Cuban couldn't bring in some younger and better players over the years. It seems as if he always brings players up for a short-time and is not really trying to build up a team that remains together over many years. I mean who else besides Nowitzki and Terry is really on that team since 2006?