Why would someone turn on and off their message read receipts constantly?

I work in a business as an assistant and was messaging this new foreign business partner. The manager was also “messaging” him via WhatsApp, but it was actually me sending the messages, yk like an assistant. I was told what to send etc. But I noticed that the business partner’s read receipts was being turned on and off since my chat with him has no read receipts or “blue ticks” and the manager’s chat has them. I have my read receipts on. I don't know I found it quite strange, and just wanted to pop on here and find out if this is something that people commonly do? He was quite pleasant with me via chat and not rude in any way tho.
Why would someone turn on and off their message read receipts constantly?
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