I agree with you completely, but “Most of us paid some money for the app”: I didn’t know it was possible to pay for WhatsApp. On what platforms does it cost money?
If they'd start asking for money now there will be a mass migration to any other free service. We did it many times with instant messengers on PCs in the 90s and the early 2000s. People ponders about $10 vs $9 but they take no time moving from $1 to free.
iirc it had like 500mil users and less than 50 ppl in the company.