The existence of these feeds is almost entirely due to poor security practices, often termed "IoT insecurity."
If you need to view your cameras remotely, do not expose them to the public internet. Instead, set up a Virtual Private Network (VPN) to securely access your home network.
Always update factory-set usernames and passwords immediately upon deploying a new device.
Most people do not. A local NVR (Network Video Recorder) with no internet-facing ports is far more secure than any cloud or port-forwarded solution.