It's viewed as a betrayal of whatever ethical/moral core Google claimed to have originally, at least by employees and customers who bought into the hype early on and didn't realize that Google is ultimately just another big tech company with shareholders.

As a former employee it never really surprised me that the company would want to move back into China, but it did surprise me a bit that they were doing so under heavy secrecy. I suppose in practice they were right to want to keep it secret (employees were unhappy) but on the other hand it's impossible to keep secrets in that company so they should have known it would leak eventually.

Microsoft, Apple, etc. doing business in China is unsurprising in comparison since we all know what big tech companies with 10k+ employees are about: Making money.