My history is your history
Except that it isn't...
Some people have privacy and security concerns, even though Comcast insists the public and private Wi-Fi networks are entirely separate and shielded from each other. Others worry that the public network will affect the private network's performance. Comcast says this isn't so.
In NL, some ISPs are doing the same. It's even a different public-facing IP address.
Of course, you can also turn it off. Though turning it off on your modem means you don't get to use it yourself on others' modems.
Comcast says it's fine and they would never ever ever possibly lie to get people to do what they want.
Buy this rock I have. It keeps bears away.