totally doable to have many USB webcams connected to a single computer.
HOWEVER
Can your computer have more? multiple of your particular webcam? that depends
see numerous prior threads on this
- USB Root Hub overload
- cheap USB webcam with piss-poor drivers
in your case, if I read that CPU correctly, your CPU is simply too old and slow to process multiple video inputs. real-time video rendering is computationally demanding. Offloading that rendering to a dedicated chip (usually, GPU offload) helps (most of the time).
And laptops more subject to thermal throttling than desktop, typically.