They scale well in the sense that they display the same thing at different sizes without loss of quality. But that’s not the only thing that matters. The primary goal of an icon is legibility.
A large text editor icon might have a pad with a pencil, squiggles on the page, rings binding the pages at the top, etc. But if you scale that down, it might lose legibility.
For good icon design, you don’t want the same thing but smaller, you want fewer, simpler elements. So you might drop the rings at the top, then as you get smaller you might drop the squiggles on the page, and if you go small enough, you might want to change to just having the pencil.
Most people don’t bother with this. They just shrink things down. If that’s what you do, then SVG solves that problem. But that’s not great icon design. Great icon design needs to adapt to smaller sizes, not just grow and shrink.
A large text editor icon might have a pad with a pencil, squiggles on the page, rings binding the pages at the top, etc. But if you scale that down, it might lose legibility.
For good icon design, you don’t want the same thing but smaller, you want fewer, simpler elements. So you might drop the rings at the top, then as you get smaller you might drop the squiggles on the page, and if you go small enough, you might want to change to just having the pencil.
Most people don’t bother with this. They just shrink things down. If that’s what you do, then SVG solves that problem. But that’s not great icon design. Great icon design needs to adapt to smaller sizes, not just grow and shrink.