Hi,
The industry as a whole never moved to cellular in laptops, probably because it was a phone communication protocol originally, cost was very prohibitive, and cellular data speeds were extremely slow by comparison (similar to satellite Internet). Now, we are starting to see other devices like tablets and even vehicles adopting cellular data technology. And speeds are improving, especially over the last 5 years or so with 4G/5G. Who knows if the industry will ever move to cellular in laptops.
An example of how Internet Sharing can be used is if you don't have Wi-Fi in a location, but have access to Ethernet connectivity. You can create a Wi-Fi network through your Mac that other wireless devices can connect to. Or, you can use your Mac's Wi-Fi connection to share Internet to older devices that don't have Wi-Fi, by connecting them to the Ethernet port of your Mac. Not may people use that feature at all, but it is there.
C