In fact, many hospitals can't compete with national chains. That's why they have formed partnerships with such clinics as a way to get their brand associated with all phases of medical care in the communities they serve.
So if it's smart for hospitals, it's also a smart idea for primary care practices—especially those with the size and scale to look for ways to collaborate instead of compete. You won't make money on the clinic itself, but you'll certainly find that patients will think of you when they have minor ailments as well as bigger ones. Alternatively, you could develop after-hours access on your own.
Obviously, the conundrum is figuring out how that can be done cost-effectively. But unless physician associations are successful in outlawing such clinics, they will have to find a way to compete because it's about serving patients when they need to be seen. The bottom line is that under a system where more people have insurance, and where lower-tier medical care has become commoditized to a significant extent, being available to patients outside of normal business hours seems essential for primary care physician practices.
That is, unless you want to work for the local hospital—or CVS.