why would anybody want ESC . to remember "&" ?

[Dan Jacobson]

$ bla1 bla2 bla3 &
$ <ESC .>
$ &

Why not
$ bla3

What value is remembering "&".

Emacs' doesn't, and doesn't bother even mentioning it:

C-c . runs the command comint-insert-previous-argument, which is an
interactive compiled Lisp function in `comint.el'.

It is bound to C-c ..

(comint-insert-previous-argument INDEX)

Insert the INDEXth argument from the previous Comint command-line at point.
Spaces are added at beginning and/or end of the inserted string if
necessary to ensure that it's separated from adjacent arguments.
Interactively, if no prefix argument is given, the last argument is inserted.
Repeated interactive invocations will cycle through the same argument
from progressively earlier commands (using the value of INDEX specified
with the first command).
This command is like `M-.' in bash.