Of course they offer interesting things because it is a marketing strategy, promotion so that their casinos are crowded with visitors. In fact we go to the casino to gamble 2 things we will meet, lose or win.
Probably it's just the way that they are saying it's either they can earn or gamble. Both of the two things you are talking about are the outcomes, but the two things you need to consider is that when you invest, you can gain profit from other players losing and on the other hand, where you play and gamble, you can gain profit, taking from the Casinos bankroll. It's just vice versa, but the better advantage is on the casino, so you could invest in a way.
Maybe some gambling sites has formed a partnership with investment which promotes within the site same with the investment site that maybe promotes also the said gambling site. This is also to encourage more people to gamble or to invest on the same time. A marketing strategy indeed.
Investing on gambling site is quite profitable you can invest your money in bankroll of some of the gambling wesites where you can make profits in percentage of the total earnings from the site.
For example you can invest on
Bustadice gambing site here.
It could be an advantage over other sites that you could invest. Some gambling sites don't offer that kind of thing, so if you check out that site, you would know that there are a couple of sites you can invest too, and make you feel part owner and hoping to profit from it. It's just that, we all want to earn but we cannot completely fulfill it if we're not disciplined. We should invest for the long run.