Blitz based on time and mental gymnastics
why are high rated players not taking my hanging pieces

Hmm. They may have been distracted, or there may have been a long term disadvantage to taking the hanging piece.

1550 could have missed it. 1800, likely, it was wrong to take for some reason. Though, if I had to guess, even 1550 prolly had a reason...

Maybe they were just pressed for time. If a capture doesn't look right in a blitz game sometimes it's better to avoid it entirely than seriously analyze the position and take up valuable time doing so.
I was in a blitz tournament my rating was about 1000 I faced a couple of 1550-1800 and in one of my games I hung a lot of pieces because i was distracted but my opponent took none of my hanging pieces
My OTB classical rating is in the 2000's. In Blitz, if it is a tactic that is thematic for the position, I will highly likely see it and may even have been building for it. If it is a loose pawn due to a random move where the move protecting it should have been automatic, then I can miss it. Stuff happens in blitz especially since I'm playing mostly schematic moves without rechecking the position every move. I'm human as are many others! Bill
In a blitz game (or any game for that matter) if you already see a clearly winning plan there is often little incentive to try to find one faster. My only brilliant move (it was in a daily game) was due to seeing how to force a clearly won endgame and totally overlooking simply winning a piece (that was not the brilliant move but the following move was brilliant).
I was in a blitz tournament my rating was about 1000 I faced a couple of 1550-1800 and in one of my games I hung a lot of pieces because i was distracted but my opponent took none of my hanging pieces