I feel the same way. Unfortunately friends and family just doesn't use anything other than Whatsapp. I've tried moving some of them to signal but they were back on WhatsApp within a week or two.
I just stop communicating with them. I know, it's not always possible, but I figure with other adults I can make it painful for them.
I despise SMS, yet people continually chat with me there. When they don't hear from me I let them know I never got their messages, so the can see first hand how bad a tool it is.