I think this is why so many online casinos don’t invest in app development (and instead focus on optimizing the site for mobile browsers)… I think they already know that players tend to focus more on the desktop experience than anything else. So paying a big sum for an app seems like a waste of money to them.
To think of it, there is so much process involved in mobile app development and it's maintenance. The casinos already have other costs that comes from maintaining the website and its contents , a mobile app will only increase their cost of operations.
Compared to their websites there will be more people who visit their their website than those who would download the app to play. It is a waste of money.
Besides, if a popular casino launched their official application for people to run on their phones, there is a chance the installation package (APK) to be manipulated by cyber criminals and then use the infected package to fish the accounts of thousands of people or even brick the phones of their victims, if the don't accept to pay for ransom.
So casinos have also decided not to focus on applications, so it is one less path of attack for hackers and those who try to massively fish others.
In the end of the day, it is easier just to manually write down the url address on the browser and let the session to start without any further hassle.