Those licences were granted when there was no FM, no internet and when there were barely 500 or so stations in the whole nation. The purpose of a higher power AM station today is to provide a listenable signal day and night in each one's market area.Incredibly stunning that you can tune up and down the AM dial in the wee hours of the morning and hear virtually the same thing on what used to be 50kW "Clear Channel" stations and hear Red Eye Radio on virtually all of them. What ever happened to having a responsibility to holding a license for such large stations but showing zero responsibility to what used to be known and acceptable broadcast standards for your city of license.
People don't listen to noisy, fading and staticy distant stations on AM at night. Like network television, people look for good programming on local stations.
Further, there are no advertisers buying time for the kind of programming you'd probably like. Heck, stations can't sell late night and overnights locally, let alone for reaching some distant area.