The more you know, the harder it is to build things. I think this primarily stems from something akin to movie spoilers: there are many things in tech that, once you know about them, they are impossible to un-know.
Performance. Security. Modularization. Accessibility. These and many other concepts, things that are typically not on the mind of the novice developer just starting to play around with creating a web application. In the mind of that novice developer, there is just a simple vision of what they want the thing they are building to look like, and 100% of their effort goes towards either making that thing or learning the new skills they need to make that it.
As a developer grows more experienced, however, they gradually become aware of other concepts, other things to factor into how they build. Things that can easily distract from or delay moving towards their vision.
They accidentally introduce an XSS vulnerability into their application. From then on they make sure to use templating libraries for all of their dynamic HTML generation, rather than just concatenating strings.
They learn about how over time a code base can develop into a giant mess of spaghetti code. From then on they make sure to organize their code neatly into modules and create separations between chunks of functionality.
They have their first encounter with a slow database query that prevents anything else from loading. From then on they always build their applications to support parallel or asynchronous request handling.
They read an article about the impact of accessibility failures in web applications. From then on they are careful to incorporate the necessary accessibility features into their projects and check for other issues.
Don’t get me wrong: these are all important elements to take into account when building excellent web applications. The things a novice programmer builds tend to not be what they would want to ship a few years later. But the higher bar inherently takes more effort to reach.
That higher bar can be daunting when starting a new project. It’s worth taking a moment at the beginning to think about your what your priorities are. For many projects the right priority is realizing your vision, and the added complexity of doing things “right” needs to wait until later.