Question about TV market size

Why is Houston the 5th largest MSA but the 8th largest TV market?

A media market , broadcast market , media region , designated market area (DMA) , television market area , or simply market is a region where the population can receive the same (or similar) television and radio station offerings, and may also include other types of media including newspapers and Internet content. They can coincide or overlap with one or more metropolitan areas, though rural regions with few significant population centers can also be designated as markets. Conversely, very large metropolitan areas can sometimes be subdivided into multiple segments. Market regions may overlap, meaning that people residing on the edge of one media market may be able to receive content from other nearby markets.

Houston doesnt overlap with other markets, especially on the edge of the market.