Default settings picked by developers to make producing the best results for most of the users of a product. I see no shame in the default value, having tidy links turned on. This feature works fantastic for 99.9% of users. It reduces the URL size, making external links shorter, and that can help with search engine optimization along with increasing conversion rates.
RealMac designed RapidWeaver to produce modern web pages. You need a web server to serve modern web pages. Just because the finder will open a browser window when you select an HTML file doesn’t mean everything on the page will work.
RapidWeaver has a web server functionality built in. If you want to test your site to see how it actually looks in a browser, you can simply Right-Click the page and select the browser you want. Not only will tidy links work, but other things link PHP will work.
This is more than adequate for most users’ testing needs.
If you want to test a website published locally, use a local web server. OS-X (Mac OS) actually comes with an old version of Apache installed. Unfortunately, Apple makes it difficult to update, set up and use (a lot of terminal stuff).
It’s much easier to install something like MAMP or XWAMP to facilitate local testing. Both work by running Apache, PHP, and a database (MySQL or MariaDB) locally from the Mac GUI. They both have free versions that will do what most RapidWeaver users need.