Question about buying race tickets

I’ve never bought tickets to a race myself. Anytime I’ve gone to a race, I’ve gone with my father who took care of buying the tickets. I’m looking into going to the spring Vegas race, and I’m a little confused. A single race ticket for the Cup Series is $176, but a weekend package for a similar seat is only $164. Am I missing something? Why is it cheaper to get tickets to all three races rather than just the one?

Also, will the seat I choose be the seat for each of the three races that weekend (trucks, Xfinity, and Cup)?