Subject says it all. There are more than a few Pokemon that don't get abilities that make sense for them, for whatever reason. Sometimes it's an oversight, sometimes the Pokemon is from an older generation and already had less fitting abilities that didn't get replaced, sometimes certain abilities would just make a Pokemon overpowered, and other times it might be a newer pokémon where they worked really hard to give it a signature ability. But either way, some abilities with certain Pokemon just makes sense. I'll start:

>Tangela line getting Tangling Hair
>Sandygast line getting Arena Trap, Sand Force of Sandstream
>Triage on the Chansey line
>Normalize on Type: Null
>Voltorb line getting any of the Electric absorbing abilities
>Rotom forms getting abilities that aren't Levitate (like Refrigerate for Frost or Storm Drain for Wash)