Most of these "we didn't get the results we wanted, we should sack the manager" type of questions and actions do not really reflect on the step afterwards and that causes a little bit of a trouble. I am not saying that it should be an easy task, but it needs to be carefully planned for the future.
Like let's assume they fired him, who are they going to get at this point? Are they really sure that they would be able to get someone that would be as good as him, or even better? I am not sure that many exists, Tuchel is the only one I can think of and I really doubt that they could get tuchel, both because of price reasons and he would rather go to a bigger name club too.
High pressure for Allegri after several match failure and last two games before success made all public want to sack him quit because Juventus won last two games at domestic and Champion League. Bad started on Serie A and loss two games at Champion League made his position as Juventus manager got higher pressure actually from Juventus fans want him sacking as soon possible. But I think all expected fans want to sack him slowly gone after success give two won for Juventus from Bologna at Serie A and last won at Champion League after defeating Maccabi Haifa.
Have another higher pressure for next weeks if Juventus failed against with Milan, actually will be at the end this season pressure for Allegri, when Juventus loss all pressure want Allegri left his position, but later he win two or three match and make public voice as him sacking will be silent awhile.