why do I never improve?

There is always hope. If you just learned the game, keep doing what you are doing. If you have been playing for some time, then pore over your games. It is not a stupid move you made. Dig out the reason you made that move. For example, you moved to an unsafe square. But why did you move there? Look for the reason you played a move. Good luck.

I would say the opposite is true. Over the last 90 days, your rating has been steadily increasing at an impressive average of around 100 per month! Were you expecting to improve faster than that? Additionally, your rate of improvement is expected to decrease as your rating increases, so do not get discouraged when that starts to happen. Unfortunately, chess improvement is a marathon, not a sprint.
I would add, after looking at when you win and when you lose, to play longer games if you wish to improve. GM's can play fantastic chess at 10 min a game. We cannot. Non masters need more time.

"Reasonably intelligent" is fine, but everyone knows that Chess requires an IQ of 120 to be played decently.
I just checked your history in puzzles, and I think I found a pattern. You often think for only 8 (or 10 or 14) seconds, and you make a bad move. I hazard the guess: this is exactly that happens in your games too.
At your rating, just focus on not giving out freebies and spend that few extra seconds to see if they have a strong reply. Opening seems acceptable, midgame has a lot of mindless moves and queen too exposed.

"Reasonably intelligent" is fine, but everyone knows that Chess requires an IQ of 120 to be played decently.
I am IQ 149

"Reasonably intelligent" is fine, but everyone knows that Chess requires an IQ of 120 to be played decently.
I am IQ 149
I am proud of you, welcome to the big brain club.

Just don’t hang material - even at my level, people hang stuff. Just double check every move.
Gaining 100 points a month is very impressive. Two years ago, I was 600 rated on here and improved to 1200 in a year (so your progress is amazing compared to that). Keep working hard, enjoy the game, play otb, read some books - that’s the only advice I really have.

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Wow. Lots of great comments! That chart really opened my eyes; I am improving.
cerebov: You're right I do move too quickly at times.
I do need to play some longer time controls. I just like that if I have a bad game I can play another one quickly, rather than spending 30+ mins. on one game.
At times I have blind spots. I had a game where my opponent had a pawn on the 2nd rank with several pieces around it. I spent two mins. and never realized the pawn itself was unguarded and that I could take it safely! Ugh. oh well, guess I need to cut myself some slack.

100 rating a month is definitely improvement. Though as others have stated, just playing blitz is definitely not the way to improve. You could do this forever and find your rating stuck at maybe 1600 rating for the rest of your life. That being said, it's important to start analyzing your own chess games and figure out your mistakes. Have a notebook on the side and write down the common mistakes you or your opponents make and vow never to make them again. That's what helped me improve so fast.
If you need help learning how to analyze your own chess games for free and easily, check out this video over here, https://www.youtube.com/watch?v=ZfG6xQvx_38
and if you need help with any other topic, feel free to ask. I am happy to help.

Someone mentioned playing longer games, but I've found that faster games have helped me to spot the common chess tropes more quickly so I don't fall into them. For example, not noticing that the knight on the 5th rank is about to fork your king on rook. Or more easily spotting common checkmate "shapes" so I actually notice when they're being set up on me (or when they are available to me).
Lol your less than half the OP's rating in both bullet and blitz. Id take the NM's advice