Different cultivars have different growth habits: some turn green early in the season while others are still dormant; some hold their green during the hottest part of summer while others die back during that period, etc. It's not uncommon for a turf to be a blend of cultivars. I believe the blend I used was a mix of a fescue, KBG, and maybe some rye grass..?
The blend for a specific area might vary depending on the specific attributes sought if it is professionally designed for a specific application (a high end sports field, or a golf course, perhaps). For a home it's probably an unscientific "some of this, some of that" or a professionally-designed general-purpose blend. I couldn't say whether the bagged products at national-name home centers use the same blends across the nation or are mixed based on regional-level climate norms.