From the comments...

Inspector: Paola was never as tightly attached to the other murders as the trio of Colorado Springs, Monmouth Ill. and Ellsworth. I could never see why that was the case. I was impressed by the second potential victim in Paola. That the killer did not seem to be satiated by one murder always seemed to me to be an interesting link among the murders. This double event was true with out question
in Colorado. Both Paola and Ellsworth shared a similar link though it was only
an attempted break-in. I don't know of such a second event in Monmouth but I
haven't studied that case to any depth. Villisca also had a potential second
event although it was largely ignored by investigators. At 2:10 A.M.
(after the murder had probably been committed) a young telephone operator was resting at her upstairs switchboard when she heard someone quietly climbing her stairs. She heard this stranger enter her hallway and saw him try her door. Finding it locked the stranger crept down the stairs. I have always wondered if it could have been the serial killer looking for another victim just as he had at some of the other murders. Ed Epperly

(Emphesis mine)
When it comes to the midwest axe murders the Hudsons deaths really are an after thought. Why is this? Why didn't the investigators at the time link the Paola crime to the those that came before and the one that followed? I have a few ideas and none of them have to do with linkage blindness. The first factor was likely publicity. Each of the previous crimes had at least two weeks of follow up and rumor to report. As the crimes contined to go unsolved, demand for authorities to "do something about it" grew as did rewards. By the time Paola occurred it had been eight months since the last (remotely) connectable event had occurred so many people had forgotten about the others. Then five days after Paola, any momentum it may have had in the press was literally swamped by the events in Villisca. A second factor may have been the body count. When Paola was discovered the nation was still transfixed by the sinking of a New York bound passenger ship in the North Atlantic; two deaths compared to over 1500 just wasn't that impressive. The third, and I think this is probably the most important, was Anna Hudson herself. Anna's reputation was very poor, deserved or not, and probably did more to derail the investigation than any other factor. The Kansas City detective on the Hudson case was dealing with a love triangle, plain and simple. The detectives on the other cases where chasing a homicidal hobo (and eventually a state senator). Still, as I said in my reply to the above comment, for all the similarities between the cases, I'd sure like to know the differences.