Because then they have the option of readding you to group chats and sending you messages
ETA: there is no way to really uninstall Whatsapp around here because so much of society runs on it, the most I can do is move all of my private existence elsewhere and hope that decreased traffic will do something
Please allow me to be devil's advocate here (and FYI, this comes from someone living in a country where government officials use [official state institution]@gmail.com to ask you to send passports and other info, and tell you they'll whatsapp you your papers when they're ready).
I have not yet been in a situation where you CANNOT skip WhatsApp - since having someone be your one-time intermediary is almost always possible. Can it be an incovenience ? Yes.
How much would this inconvenience compare to what my grandfather's grandfather would consider an inconvenience? Probably not much. (You mean, I had to twiddle my thumbs for twice as many minutes!? How difficult)
So in the end, you're asking people to experience what they consider to be a major hassle (having 2 apps) just for you, when you're not willing to go through the pain of having just one app. It feels unbalanced.
So please consider that people might be complaining that you're being too much of a Don Quixote, but actually, the reason it's not working is because you're not playing the Don Quixote card hard enough
ETA: there is no way to really uninstall Whatsapp around here because so much of society runs on it, the most I can do is move all of my private existence elsewhere and hope that decreased traffic will do something