Definitely a strange one but unsurprising considering De Laurentiis has a history of attention seeking & off-the cuff decision making.
He initially didn't agree with Sarri's request of a bigger transfer budget this summer, but I doubt Ancelotti will be any cheaper with his wage demands & requested players that are currently Vidal & Di Maria.
De Laurentiis could have back Sarri which I think would have been cheaper in the long run & play attractive football which would have eventually won trophies which he craves. But he went down the easy route with a more pragmatic manager who probably will win Napoli a trophy or 2 with investment which I think would have been more sustainable with Sarri since Ancelotti will inevitable leave in the short-term as per his historical managerial career suggests.
On the other hand Sarri to Chelsea in my opinion is a bad fit. Its a club that historically demands instant success & even if you do you still get sacked. As someone mentioned earlier, to go from a rather defensive Conte team playing mindset to Sarri's possession based football will take time. Furthermore, Sarri just like any manager has flaws with the biggest one his lack of squad rotation & man management skills with players outside his preferred 11. A good example of this was last Sunday in the last game of the season with a meaningless match he didn't bother to put on even for a few minutes Christian Maggio a club stalwart in his last season for Napoli who had been at the club for around 10 years totaling 233 games. Its also the reason why Napoli burnt out during the scudetto run where he constantly played his best 11 all season even against lower league clubs which if appointed he won't get away with at Chelsea.
Regardless of this, he brought joy to his refreshing approach on how to play attractive football in Italy which has been crying out for a remodel on a national level for ages. However, will he change his stubborn ways, I'm not so sure & time is not on his side since he's entered football managerial status relatively late in his life approaching 60.