What’s the switching cost? If all your friends are suddenly available on your most essential communication app, what’s the reason not to give a try. And boom you’re locked in
Switching cost is not high, I agree. The main thing is connecting whatsapp to your bank and credit card accounts. Some people might be hesitant. But there's another issue that is not so much related to switching cost. Whatsapp is a communication app. People mostly use it to communicate with friends and family. Not everyone wants that any stranger who they ever send or receive money from would now have their phone number and can now see when they are online and text/call them on their main communication app. (you can obv block users to prevent that but still). Although tbh I think this wouldn't be a big issue for the cultures where whatsapp is currently very popular as they are already using it to communicate with everyone.
I don’t think the sending money to businesses feature will require you to disclose your phone number. WeChat doesn’t, and that app is a privacy nightmare.