The reasoning behind the online casinos giving players money is how else would they get you to sign up and see their games. Unlike when you walk into a casino where you can view all the games they have and if you do not want to stay you just walk out. Online you must take the time to download the software where you will see everything they have instead of going on a mobile or flash site where games a limited to just the more popular ones or newest. So this is like a thank you for giving them a chance to show you what they can offer you in gaming. Now you still can just delete the casino if you do not like it but before you do it might be wise to play the free money and give the machines a chance. You never can know what will happen, you may win or you may lose but either way you are not out anything except your time. Most people waste a lot of time on the internet anyways.
Not ever casino will give you money and not many of them do when you play on mobile devices since you can instantly play they figure there is no need to give you anything for that. They will give you money on a purchase if you decide that is what you want to do. The best sites do have a small incentive but it is no where near as much as downloading in most cases. It does make it really hard for people when they see a free money offer and then they go there and the promotion doesn’t exist, this is normally to be only available when you download and it is hard to separate the different ways of accessing the casinos. So most just show what you get when you go on your computer to visit and leave the mobile promotions as whatever you can get. If this is your only means of accessing the web then you will accept that the promotions are different.