Taking a "prisoner" is an extremely dangerous thing to do. You're putting your own life in greater danger by attempting to capture and hold someone it seems to me.
Yes, yes indeed. You could be (1) overcome by the perp; (2) shot by a first responder; or (3) ambushed by one or more accomplices. All of those things do happen. And then there are the dangers inherent in the aftermath.
Those include the little problem of liability. In making a citizen's arrest, you have all of the liability that the police department has. You can be sued for use of excessive force (there's a criminal aspect that, also), and you are potentially liable for any injuries or problems the perp may suffer starting after you effect the arrest. However, unlike a sworn officer, you are not indemnified by the community against the civil liability.
You are on your own.
The dangers are physical, criminal, and civil, and each can be overwhelmingly severe, and they can impact you in combination. There's a whole lot to lose indeed, and when you stop to think about it, there's very little to gain.
A citizen contemplating effecting an arrest lacks training, back-up, another partner to assist, direct communication with a dispatcher, approved policies to follow and to point to afterwards, and as mentioned above, indemnification.
Frankly, I cannot understand why anyone in his right mind who understands what he could be getting into would even consider trying to trying to hold perp.