Promotions, they are often running for various reasons. But they are not profitable and in fact no slot game is. The profit is only for the casino. These free bets are only to lure you into the false confidence of being able to win but it does not happen like that or else the casino would have already gone bankrupt several years ago and slot machines would not exist.

I admire you enthusiasm but I must warn you to see players on physical casinos first before you start to put in money, often in Vegas, theses guys started playing and have never been able to come out because they lost so much money.