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.
I think the problem is not the customer's benefit, the problem is the resources and benefits from the casino, it can be seen that the use of mobile devices is increasing in this convenient society, if a suitable application is created, it is possible to expand the casino's benefits but a compatible app seems to take too long, especially with so many different platforms on the phone, it takes a long time to get a non-malware certificate for the phone. Especially if the government network can prevent this plan from running smoothly, such a situation will make the feasibility of the gambling application low and unattractive.