RUMOURS IN A NUTSHELL

According to the source:

Battle for Azeroth is shorter because there were many delays during the development;
Patch 8.3.5 was dropped because the studio had no time to prepare it;
As many as 40% of content was removed from patch 8.3;
The pressure from superiors caused patch 8.3 to be released too early (without thorough testing), which resulted in a lot of issues;
Patch 8.3 was supposed to look completely different and provide a better ending to Battle for Azeroth.
The failure of patch 8.3 is a bad sign for the upcoming Shadowlands expansion;
Several graphic artists were supposed to leave Blizzard because they did not feel appreciated and their works were thrown away.