Scratch is (I think) intended for use for executing 'this session' elisp code as the buffer is set to lisp interfactive mode, not intended for where you store your scratch text.

Other buffers behave differently, maybe scratch isn't useful for a large number of emacs users, however scratch is working as designed.

There is a remember-notes feature that isn't deleted [1]. Or you could just set up so you can't kill scratch (see first answer in [1]).

[1] https://emacs.stackexchange.com/questions/19254/never-close-...