It makes sense for casinos to try to implement fast paced games because in that way they increase the amount of profits they get while reducing the time they have to serve their customers, however from the point of view of gamblers it is better for them to be able to gamble for as long as possible while using the smallest amount of money that they can while at the same time they remain entertained, and this will mean gambling in games which are more engaging and more fun to play.
You are correct that for casinos it would ideal that people gambled as fast as possible so they can carter more people.
Actually this reminds me the era when arcade businesses were at their peak with those arcade machines with games of high difficulty so children would play and lose fairly quick in order for the shop to earn more money.
However, in these times online gambling is getting so prevalent that casinos can take advantage of the fact they do not need to physically hold machines in order to carter players, we all run those games on out PCs now. Once such limitation is erased it becomes easier for online casinos to offer games that can be relatively longer in comparison to classical ones found in real life resorts.