Why would an airport be depicted with symbology for runways longer than 8,069 feet even though it is reported on the sectional as 7,200 feet?
The FAA chart user's guide says:


   Hard-surfaced runways greater than 8069' or some multiple runways less than 8069'


It's the latter case of some multiple runways less than 8069'.



This is also confirmed in the post, "What is significant about the number 8069 ft?"


  Specialists also place these polygons around the runway pattern of aerodromes with multiple runways that are less than 8069 feet, in cases where the multiple runway pattern does not fit into the largest, circular aerodrome symbol.


(FAA FAQ; emphasis mine.)

Most likely MKO doesn't fit in the standard circle  because of 36-18 and/or 4-22 intersecting the circumference.


(Chart Supplement via skyvector.com)