Why should someone pay for your designs? Because you have talent, knowledge, invested time and you can create something unique that someone else can't. The same is true for type designers and their product.
They don't give away their quality product for free because the invested a lot.
Most free (gratis) fonts are very low quality. Imagine doing an identity for a startup with a gratis font, but soon they will expand into other countries. Then you discover that the free font you picked doesn't have the language support your client needs. What will you do? Hire someone to design the missing glyphs for you? Edit the font yourself? Most free fonts are still licensed and often editing isn't allowed. Maybe you can redesign the company's identity for £30-50? Now you regret not buying a proper font in the first place.
There are very few good, free fonts. By "good" I mean: big glyph sets, multi language support, hinting, spacing, kerning, range of weights, true italics, small caps, table figures, fractions, ligatures, swashes, etc. If a font like this exists, it will be overused.
You seem to understand difference in quality. "Looks just as good" is the wrong comparison. Some fonts are display fonts, used to draw attention, and they are applied in big sizes. Then you have the workhorse typeface for setting text which should work well in all situations. Legibility is also important. The requirements of these two are very different. Most free fonts are very useful but only "look good" to draw attention; they aren't workhorses.
You say never to have bought a font. Thats probably not true. Most systems and a lot of applications come with fonts. A lot of these fonts are not free have a licence. If you paid for software that bundles fonts, than you also paid for those fonts.
Like Scott said: "You really do get what you pay for." If you can't see the value in paid fonts, then you should stick with free fonts.