I mean...
作る ----> 作らせられる (causative passive) -----> 作らされる (shorten form of causative passive)
話す ----> 話させられる (causative passive) -----> X 話さされる
Ah, I see. You were talking about another form of the causative passive like as "行かせられる vs 行かされる," "取らせられる vs 取らされる."
Exactly, ichidan verb like 食べる generally doesn't take this form. Also, -す ending godan verbs like 話す are rarely abbreviated, too, since they have the same -させる ending causative forms.
食べる --> 食べさせる(causative) --> 食べさせられる(causative passive) 食べさされる？
足[た]す --> 足させる(causative) --> 足させられる(causative passive) 足さされる？
FYI, the causative passive forms can be used as the causative potential, because the causative form conjugates as an ichidan verb. (The potential form and the passive form are the same in ichidan verbs.) However, this abbreviation is occerred only on the causative passive.
母にニンジンを食べさせられた。
I was made to eat the carrots by my mother.
彼女だけが彼にニンジンを食べさせられる。
Only she can make him eat the carrots.
もっとお金があればお前を大学に行かせられる。(× もっとお金があればお前を大学に
行かされる。)
If we have more money, we can let you go to collage.
買物に行かされた。
I was made to go shopping.
私はとりとりべさんのように日本語が上手くに成りたい
It should be either 日本語が
上手[うま]くなりたい or 日本語が
上手[じょうず]になりたい.
Thank you.
But, uh, I'm a native Japanese...