The absolute majority of people come to Entropia Universe after googling “how to make money while playing a videogame” or something similar, they see the huge HOFs others have gotten, in fact some don’t believe those are even real. After people realize that they won’t be able to get rich from it, some quit, but some stay and continue investing into their avatars because of the RCE aspect and the thrill, which make EU unique in the gaming industry.
If returns are fixed at 90% you take away the highs and the lows, which means that essentially the other 10% is what you pay for your subscription, which you can also purchase with in-game currency if you do things right.
In this case most people will have no desire to keep playing, because 90% returns upfront is not appealing to those that are in for the thrill. Many want the possibility to hit it big while never knowing what they are going to find, even if it means that actual returns will be less than 90%. The thrill is what gives EU an edge over every other game, if you take that away, then what do we have left?