Rewatching TVD for the 50th time

Every time I watch I have questions and comments. First of all, Isobel is a freakin genius. Her ability to locate vampires isn't mentioned enough, especially by the other characters. She found Katherine when Klaus couldn't do it over the span of 500 years. Which brings me to my question. Why is it that Klaus wasn't able to find Katherine but Isobel seemingly could without much of an issue? Is it because he stopped actively searching and relied mostly on reports from minions/suck ups? Or is it just indicative of Isobel's skill?