Tuchel was removed because he was a remnant from the past owner of Chelsea. The new owner needed someone who he could believe in as the right choice, but clearly he has made a mistake with Graham Potter. Bad thing is that Chelsea gave him a five year contract and to let him go now will mean them paying him off hugely since they are the ones breaching the contract. They have spent a lot this season and know that letting Graham Potter go will cost them more money, so perhaps the best choice for the business is to give him some more time maybe till next season.
During the time when they sacked Thomas Tuchel, I did say that they will definitely feel the hit and regret on that decision as time goes on and now it already happening.
Potter poor performance now has become worst than Thomas Tuchel poor performance time that lead to his sudden sack.
Chelsea is a big team for Potter to handle and with time if things continue this way, I do think at some point the owner would be left with no option than to sack him.