Have to setup port forwarding to make it available outside your network.
I tried running it off my main PC for awhile, but it’s kind of a pain and impacted my gaming sessions. Moved it onto a $400 Lenovo server I got off eBay to great effect. Used unRAID to setup a simple server for it. Lots and lots of guides out there for it with a great community. Have since upgraded beyond that server, but it was a great start.
Sims is pretty popular and the main version everyone plays is PC only, but can be run on laptops and other low end PCs. There are a lot of ‘I only play Sims’ people out there. Could account for some of the numbers