Cost is most often directly proportional to quality, and quality is directly proportional to reliability, and reliability has a directly proportional relationship with survivability in a gunfight.
Besides, smaller, more compact weapons cost more to manufacture and it just so happens that smaller, more compact weapons are better for every day carry.
A person doesn't need a Rolex, but I wouldn't use the watch that came in my Froot Loops this morning to coordinate a mission to the moon, either. That's what Speedmasters are for.
I want to replace that $750 at a later date, rather than have the option removed for me.