I have explained the reason enough times. I don't think there's more to say.
Fair enough. I did not respond to your points.
In the short term, risk can be a cost, or it can be a benefit. That's the nature of probabilities. In the long term risk may be a cost or it may be a benefit, depending on the alternative. In D&D 5E, rolling for stats is a benefit in the long term (because the expected value is higher than the standard array), and rolling for hit points is a cost in the long term (because the expected value is less than taking the average rounded up).
Many people aren't good at realizing this.
That's not my problem. Understanding the risks you are taking is part of playing a game. Understanding that a 4 is probably going to come up less often than a 5 in Settlers of Catan is part of playing the game. Understanding that rolling for hit points is probably going to leave you with less hit points at high levels is part of the game.
Presenting risk as the fun choice, where the fun is the reward, is equivalent to hiding that risk. (Cue every lottery and casino ever)
This is false. Nothing is being hidden. While the rules are not totally clear about the probabilities, they are clear about the mechanics. Most of the probabilities are very simple, and for the more complicated one like rolling for abilities, there are plenty of resources online. No lottery I've ever played in has hidden the risk. The probabilities are freely and publicly available. Everyone knows about the casino's edge. In games like roulette, it is easy to know exactly what that edge is. Lotteries and casinos take advantage of people, certainly, but not because they are hiding anything.
Hiding and/or not compensating for cost is an unfortunate design decision in a role-playing game.
Again, nothing is hidden. So the question is, should you compensate someone for taking a risk. Specifically, in a role-playing game, should you compensate someone for rolling dice instead of taking a set value. That is, should the expected value of the roll be higher, equal to, or lower than the set value. You are saying it should be higher than the set value, and I don't think that you have given a good reason for that to be the case.
Let's take rolling abilities scores. Some people want to roll ability scores because they want to be better. Better than what? Well, it ends up being better than the other players. I don't see that rewarding that desire is a good game design choice. Now, not everyone who wants to roll ability scores wants to roll them for that reason. Some people want the dice to lead them to a character to make. I don't see a need to penalize those people for that choice, but I don't see a reason to reward them for it either. I am not aware of a desire for rolling abilities that justifies making rolling more beneficial in the long term.
Hit points is more problematic. Since the expected value is always fractional, while the allowed values are always integers, the set value has to be higher or lower than the rolled value. I am fine with the set value being higher. I would prefer a mechanic where the set value could be equal. For example, if you could reroll all ones for hit points, the set value and the expected value would be the same. And I think
that would be the good design choice, where one choice is not better than the other in the long term.