It would mostly depend on the mood. Sometimes you don't feel like sitting on a chair, using a mouse and a keyboard to play some games, so in such times, it's great if you have a mobile app of your favorite casino that you can use while either laying down on the bed or on a couch and enjoying the experience. It is also convenient if you are outside, maybe somewhere waiting for someone or something, like in a restaurant or a cafe, and you feel like you should do something to kill some time if you are alone; mobile gambling apps can come in handy in such situations too.

Other than that, most people usually like gambling on their PCs because as you said, the experience is much better, you have a bigger screen, better visuals, and you generally enjoy it more. The reason why most platforms don't focus on developing mobile apps is because there is not enough demand for it, so they don't prioritize it.