With the size limits that is simply the way it is at Pueblo. Sometimes you get lucky and hit a few bigger ones, but most will be under the 18 inch limit because when they get close to 18 inches people keep them. So the size distribution is truncated - only 3% to 5% of the Walleyes in Pueblo are 18 inches or longer (and they get caught dozens of times before they get that big).
Enforcement historically has been minimal, so lots of people don't even measure their fish! It has improved a little over the last couple years, but there are few game wardens in Colorado so they only do random checks now and then (the last couple summers I have been checked a couple times each year on the weekends - I fish there most weekends.)
All I can tell you is keep plugging away and eventually you will catch a limit - it's a numbers game. (Experiment a bit when you are catching fish because sometimes the bigger fish want something slightly different.) Forget the old rule that bigger lures catch big fish - on Pueblo that is rarely the case - smaller lures tend to catch more walleyes on Pueblo; including some big ones.
Fishing is more addictive than crack. I'm addicted to fishing; just can't ever get enough....