Don't we bring in recruits for the weekend too? For that reason alone, I think the coaching staff loves having a big spring game with all of the fanfare.
Another big reason to keep the spring game is that it is a big economic boost in the spring for the city of Tuscaloosa. People tend to spend more money because they aren't shelling out hundreds of dollars just to get in the stadium. All of the places like gas stations, restaurants, and retail get a nice boost during a relatively low point in the year. I remember back when I was younger and all you could get was bottled water at the game. Now they have the concessions open as well, which has to bring in more revenue for those vendors.
I know it's not all about money...but I do know that businesses in Tuscaloosa look forward to mid April every year because of our glorified practice.