I'm not sure what their official reasoning is behind not installing something like WDW but I have 2 guess. My first guess would be because some of their rides are more intense than WDW and a little bag in front of you wouldn't hold in your stuff. My other guess though is that they want you to pay for a locker. I know the first 45 minutes is free but how many people would just rent a locker and go do all the rides for the day.
Also, I don't like the lockers either. For me I find it hard because I have Type 1 diabetes and if the wait for a ride is really long then there's a chance of my blood sugar dropping, especially in the summer, and without my bag I don't have my meter or my glucose tablets. I've had to step out of lines before because of this and I'm not the type of person that wants to push my way back through to meet up with my husband so we both leave the lines.