Why can't I stay over 200 rapid rating?


If you lose a queen (in the last 3 losses, I didn't check before that) and make multiple piece blunders every game, it is difficult to progress. In one of those 3 games you were lost after one minute of play, in others you were in time trouble.
It is safe to say that 10|0 is too fast, play at least 15|10 or even longer games, and keep trying to take your time, make sure not to hang your pieces (you still will, but you might hang them less frequently at least). In 2 out of 3 games I've mentioned, you were basically winning by having heavy material advantage, but then you just hung a queen and squandered it.
One move blunders and simple tactics are your first order of business.

Improving Your Chess - Resources for Beginners and Beyond.....
https://www.chess.com/blog/RussBell/improving-your-chess-resources-for-beginners-and-beyond

Aim to maintain a reasonable pace throughout the game to avoid time pressure in critical moments. Try to stay calm and focused, and avoid making impulsive moves or succumbing to tilt after a loss.

Don't only focus on how to move your pieces, but focus on how to make your position better every time. When you develop pieces, focus on which squares those pieces control. When your opponent attacks your piece with his piece, you can ignore it if it is protected, but then you always have to think that your opponent can capture your piece when he wants. Try to calculate when this happens, and don't let your opponent make a advantage in trade.
Also, focus on square controls of your opponent before you move. Then it will be much easier not to hang a piece.
Learning about rook endgame and queen endgame is enough for preparing endgames in 200.