All they have to do is to market their casinos. They're all doing that because they know that the market is expanding and more gamblers are coming in online.
They don't want to deal with the hassle and tiring day of going to the casino just to have the same results. At least with playing online, they can easily find their comfort at their house and relax while sipping their favorite drinks.
online or offline marketing I think all casinos do it, because to make their casino crowded with visitors of course they have to do this. with them marketing it online of course it certainly requires spending money but I'm sure in a short time the money they spend to advertise or market their casino online can be returned, moreover we know that the majority of people now tend to do activities online because it makes it easier for them and gambling is something that is quite popular with many countries or people.
you are right, it makes sense to say that they have to travel which may be tiring only for the same result which is disappointment, because that is indeed the most likely thing that will happen.
but they can get other pleasures at land-based casinos, maybe like interacting with new people there or seeing other people win or others. and for online-based casinos, it is indeed quite easy for many people to do it.