Some fans buy the media brainless thing that Chelsea is unfair with their managers. Since Mourinho was sacked back in 2007, I think its fair to say that only Ancelotti received a rough treatment.
Avran Grant - never produced a great job 10 years after he left Chelsea.
Scolari - after getting sacked he went to Uzbekistan, then went back to Brazil when relegate Palmeiras, then there was the 7-1 and he was the main reason for that result, went to China then now is back to Brazil.
AVB - was latter sacked by Spurs, then went to Russia and China.
RDM - sacked by Schalke 04 before even completing an entire season, and then sacked by Aston Villa after 4 months.
Mourinho - went to United where he had 2 mediocre seasons, and then finally sacked after the club realize he is now a mediocre manager.
Conte - we still don't know whats going to happen with him, but with the record of past managers, there is a fair chance he won't put produce any decent job any time soo.
The time showed that most of those guys were just not good enough for the job, as I said, Ancelotti is the only manager that had good results after leaving Chelsea, but lets not forget he was later sacked by Real Madrid and Bayern because both clubs didn't believe he was a long term manager.
The club's problem is not sacking the managers, in 90% of those scenarios the club did the right thing, but the problem is they are just appointing the wrong people in a lot of those cases, like Grant, Scolari, AVB, RDM and even appointing Mourinho again. Most of the current problems have their roots in Mourinho's appointment back in 2013.