So websites are usually made with HTML, CSS, and JavaScript and since .NET MAUI is built to be cross platform, does this mean I can make a website people can go to on their web browser purely with .NET MAUI instead of the standard HTML + CSS + JavaScript?
Cross-platform doesn't mean all platforms. Right now the supported platforms are Android, iOS, macOS and Windows. Tizen is also there, donated by Samsung.
In this case a platform is more an actual OS/device family. More on what .NET MAUI is exactly and how it works can be found here.
There are similar frameworks that do offer a web target along with all the supported platforms by .NET MAUI. Uno is a well-known one.