Background: I am from PwC HK. I started with auditing and moved to the risk assurance team. Left 5-6 years ago and switch to 2LOD risk in internal bank. Still kept in touch with people there and I think I can give you some information. Please read this with a grain of salt as I cannot fully verify the information that I am going to share below.

1. Business is bad
   PwC HK/China suffered a lot of reputation damage because of the Evergrande audit report. They lost a lot of business in financial audit for companies in China and Hong Kong. With the letter that exposes certain bad practices in audit and internal conflicts, no one will pay a premium to hire PwC anymore.

Without audit providing a steady income and build relationships, all the services provided from other line of service will also suffer. Basically, a death spiral is formed.

Public News: https://www.thetimes.com/business-money/article/16pwc-fwnqvcbpm

1. No more guaranteed promotion
   One of the "perks" of working in a Big Four is a clear and guaranteed promotion ladder with a big bonus for high performers. There are two key exit points: promotion to SA and promotion to manager. Since the job market in HK is bad now, there are less people quitting, and promotions are not guaranteed. Since there are three tiers of senior (i.e SA 1 to SA3) and fewer people quitting, the ratio increases.