Just as you have stated, casino owners won't want to waste resources on what they think won't be beneficial to their customers, which could be the reason why they don't value having an active app, but there are still a few sets of gamblers who love to use applications more than the web; no matter how mobile-friendly the casino is built to be, it can't serve the same purpose as the app does for them.

If it's possible, I will say casinos that have the resources should also consider app development since they are open to serving all customers.