Good point. This is an extreme example, but look at Samuel Little. He committed rapes and murders - PROBABLY 93 - over three decades and no one was making the connection.
en.wikipedia.org
One of Little's favorite reading materials was true crime magazines. Nowadays criminals have a better source, the internet.
Just because this killer hasn't been connected to other crimes doesn't mean there aren't others. He could have had something else in mind here, it went sideways on him and doesn't resemble previous crimes. He could have sat back afterwards and looked at his mistakes and future murders don't look like this one. If LE even hasn't made a connection doesn't mean there isn't any. To add to that if LE is using ViCAP (Violent Criminal Aprehension Program) to look for other crimes that is a problem. The last I looked about 10 years ago out of 18000 city, county and state LE agencies only about 1400 entered violent crimes into ViCAP. If this killer is not currently local and is committing crimes in places like Backwoods Arkansas or Podunk Nebraska chances are high ViCAP has no visibility on it.
I believe the chances are high this killer is somewhere with 1-2 hours of Delphi and has some past connection to the area. But there is also the possibility this guy could be in Kansas City scoping out Swope Park or in Columbus OH stalking Alum Creek Trail.