You have a large arena for a div. 4 team. If you get promoted, your stadium will be filled. The only way you will fill that many lower tier seats this season is if you put the price very low and don't lose any games. Remember that price changes only can be changed about 3 times a season and the next change is coming on the 27th, I believe. Another option to fill seats is to hire a stronger PR Manager. A better PR manager will improve attendance and also merchandise sales. If you look at my team, I have a minimal PR manager, a .500 team, and around 7000 seats in my arena. I get around 80% attendance. This will go up if I lower my prices and/or win more games.