And I can add as someone with a degree in psychology: There are phenomenons similar to the learned helplesness, which also neatly correspond to a totally different outcome of such lotteries. If people try for some time to get the achieved result, and they fail, and they don't even know if they could succeed anyhow, because the chance is so small, then they just give up. Such things are of course also not fun at all.
Operant conditioning works best if you don't get your goodies every time you do something, but quite often. So, if you have a reasonable chance to get something, then you will try again if you don't get it on the first, second or third time. But if chances drop, then people just stop to care. This comes along with disappointment.
There are exceptions, in cases where the reward is that good, so you are willing to invest a bunch of time (like 1% mount drops in case of mount collectors). But these are niche situations for a niche audience, specially tailored to such kind of people with a special interest. But to generalise such concepts over the whole game is a very bad idea.
And yes, just like someone here already mentionned - it is very fulfilling to finally get a reputation to exalted, or to finish a legendary questline, or to collect all mats for an expensive crafted item or whatever. Such things are quite deterministic (even with some random elements within), and they still bring the joy of reaching the final goal.
You even have a motivational bonus in such cases, because you see the progress of your achievement on various reputation steps, on the progress in the questline, or in the progress of collecting the amount(s) of material(s). In case of a totally random item, you don't have such a motivation bonus. It's an inferior solution to keeping players motivated to repeat a task.