Too expensive to implement such a system for light rail, it’s the same here in DFW with DART, they check so infrequently you can always tell which riders aren’t paying.
In my case I have an app that displays my pass on my cell phone.
Seems like the time of day has an impact. It's rare for me to get checked during rush hour, but if I head into town late or leave early, I'm a lot more likely to be checked.