How do ISPs enforce outbound traffic limits for their residential customers? Why do commercial connections require traffic shaping by the customer's equipment, but residential connections don't?

I recently upgraded my friend's office from a coax cable connection to Comcast Dedicated Ethernet fiber. Comcast made a big deal about how I needed to make sure I shaped the outbound traffic so as not to exceed the CIR (200/200), otherwise TCP traffic would be severely affected.

This wasn't a problem as we had a Palo Alto firewall that could easily do that, but it made me wonder why this was something I had to do instead of the coax connections where we just plugged E0 on the firewall into the modem from Comcast and let the ISP handle all the rate limiting? What's the difference between the two connections in terms of how the rate limits are enforced?