25 to 40 reputation phase is not the hardest at all, it gets harder (or more expensive) exponentially and that's why there are higher rewards for higher reputation, because it would not make sense to buy upvotes to get that high.

30-50 reputation originally had higher rewards, a lot of people with lower reputations got their higher rewards before the rewards were lowered because of abusers. I don't remember exactly how many were attested when that happened, but I think it was around 20k, now it is almost 50k.

So, there is NO discrimination, just simple math to make it not profitable for abusers who upvote their reputation up. It doesn't make sense to buy your reputation up when you have over 50 because at that level, getting even higher costs a lot more than the rewards give.