I can't speak to your life, but not having Whatsapp would result in my being left out of some conversations and activities I want to be a part of. Email or SMS

I can't speak to your life, but not having Whatsapp would result in my being left out of some conversations and activities I want to be a part of. Email or SMS could theoretically substitute with reduced functionality in most situations; Matrix could substitute with no loss of functionality. Most of the time the other people in the conversations prioritize their activity/task/goal/socializing over technical or ideological concerns about their communication tools, so getting them to change tools would be an uphill battle. In short, unless I'm really important to a group, I have to use what they use or get left out. If I'm the most important person in every group I'm in, I'm probably in the wrong groups.