Why did this happen?! My rapid is 1700 but my blitz and bullet is only 800!

Didn't you answer your own question?
Pattern recognition and ability to scan the board for moves quickly are vital to blitz games.

Maybe the reaction time of your brain is >1s. Go bungee jumping to kick it into gear!
You need to get better at spotting the correct (complex) moves without too much thought.
Train direct pattern recognition rather than linear thinking (if...then...) through puzzles.
Learn to see tension vectors and zone intensities across the entire board rather than individual pieces. Chess is spatial rather than particle-based.

I am 1500 on rapid (mostly 15/10) but only 1100 on blitz, and I even play blitz 5/5... I suppose it is because I recently start learning chess so when I have time to think about proper development and fundamentals I learned it is better