Why can I not get better at chess?

At your level, most games are won or lost because someone gave away free pieces, or failed to capture pieces that could have been taken for free.

The easiest way to improve at that level is to improve your tactics. This means doing lots of tactics puzzles. Puzzle rush is good too.

This will sharpen your tactical awareness and help you spot common tactical patterns, which will help you spot when there are pieces available for free with a simple tactic, and help you spot your opponent's tactical threats so you can avoid giving material away for free.

There are other things you can do to improve too, but at your level, this is the biggest one.

Don't spend too much time on openings. You don't need to get that tiny advantage out of the opening; that will matter more when you're around 2000. All you need from an opening is to reach a playable middlegame. But if you're going to spend time on openings, don't memorise specific lines, since you'll be completely lost as soon as someone diverges from a line you know. Instead, try to learn the idea behind the opening and the plan that you should follow in the middlegame. This will help you have some idea what you should do even if your opponent diverges from your prepared lines.

Learning endgames has some value too. Endgames are simplified positions, and understanding where your pieces should go in these simplified positions can help you understand where they should go in more complex positions.

A book targeting lower-level players such as IM Silman's "The Amateur's Mind" can also be good.

But the main thing you should focus on is tactics.