Think about a car.
Most of us look at the car, and can only see the body. If someone repairs some dings and puts a new paint job on the car, it will look much more beautiful. It's basically the same car, but that is all that we see.
A mechanic opens up the car, and looks at the engine. They see how good that engine is. They see that everything is arranged to be easy to get at, maintain, and work on. They see the parts and know how well designed it was. To an experienced mechanic, the engine of a well-maintained high quality car becomes a thing of beauty. They can't explain to you what makes it beautiful, but their notion of beauty is likely to translate into lower maintenance costs, a longer car lifespan and better performance. All of this adds to the worth of that car, even though you can't see it.
When you look at a website, or an application, you're looking at it like most of us see cars. When I look at code I'm looking at it like the mechanic looks at the engine of the car. You can never experience the beauty of that code like I do, it is literally invisible to you. But that beauty is important just like the mechanic's beauty is. It determines how well that software runs, what kinds of problems it will have, how easily the software can be improved, and so on. All of this adds to the worth of that software, even though you can't see it.