I think Apps is not anymore necessary as even if you will access the site through your phone, you can still view it clearly and can put your bet easily.
In many sports book that I'm using, I've never seen one that has an app, so I think its not that really necessary.
For me it is different, application has an important role in current era especially since this gambling site is a big site. Although there are no gambling sites to implement it, but if SportsBet is able to implement this means they will become first gambling site and this is a new innovation in gambling. What's more, application is able to control bets more effectively because development of increasingly sophisticated mobile applications such as PWA.
If an app has an important role these days, how many gambling sites are providing mobile phone application for their players (based on what you know)? IMO, most real gamblers will always prefer to use the main website through PC because I believe it will give better experience and gamblers can access all available features.
If gamblers want to play through their mobile phone, then mobile browser is more than enough. It is even wrong if sportsbet will become the first gambling site if they are able to implement it because there are many gambling sites (usually fiat poker sites) has mobile applications already. If you are referring to crypto gambling sites then there is a site callled BVC. I dont even think that mobile app will give better experience to gamblers.