I feel like a lot of the resistance is from people who think this is somehow bad style, because it's associated with a source of bugs in other languages. The same kind of people will argue endlessly against having 'goto' in a language, even when it can clearly make for cleaner code (eat it, Dijkstra!) in some cases.

https://pic.plover.com/knuth-GOTO.pdf

    x = stuff
    while x:
        x = stuff

    while true:
        x = stuff
        if not x:
            break

  Another motivating code pattern is the "loop and a half".
 
  It was once common for processing a file by line, but that 
  has been solved by making file objects iterable; however 
  other non-iterable interfaces still suffer from patterns 
  like:
  
  line = f.readline()
  while line:
      ...  # process line
      line = f.readline()
  
  or like this:
  
  while True:
      line = f.readline()
      if not line:
          break
      ... # process line

  Either of those could be replaced with a much more clear
  and concise version using an assignment expression:

  while line := f.readline():
      ... # process line

You clearly never had exposure to a PHP codebase. If people can trip up, people will trip up.

But c-style assignment in Python was never going to happen, not should it have.