Being stuck for months with a character that sucks is pretty bad, and saying "well you accepted the risk, suck it up buttercup" doesn't make it suck any less. Which is why I prefer "point-buy or your choice between a 4d6b3 that you've rolled or standard array".
If you're unlucky and roll poorly, you might not get the exact character you want, which I agree should not be a given, specially if you took the risk of rolling, but at least you will be competent. And, more importantly from the DM point of view, more in-line with the system's expectation. Why simultaneously make life worse for the player and harder for you?