Uncommon surnames

Why are people with rare/very uncommon surnames sometimes just as difficult to track down as the ancestors with the most common surnames (other than spelling/indexing mistakes)... is this just due to the fact that there are so few of these names that their records probably haven't been made available or indexed yet? I feel like I have the most luck finding them when I account for these mistakes, as well as search unindexed records on my own or just narrow them down further by easier to find relatives records if I can.

It's like you see the name and say to yourself, "The surname isn't Smith or Miller, this will be easy!", and yet you end up with nothing... no results anywhere instead of way too many. I admit I still prefer the rare names because I can eventually track them down, while it is statistically impossible to find a few of my ancestors with the most common names at the moment. Does anyone else have ancestors with extremely uncommon surnames that are a brick wall for these same reasons?