WhatsApp isn't just a messaging app. With its stories and statuses, it's a mini social network in and of itself.
Beyond the HackerNews crowd, most people don't care about privacy. They care about features. Signal won't be able to compete with WhatsApp unless it builds some of those features into its app.
Edit - HackerNews crowd seems to get tunnel visioned when it comes to tech products. Every response below is something on the lines of "I don't use stories" or "None or my contacts use stories".
I don't use stories either. And most millenials don't use it unless they are extroverts. But we make a small percentage of their audience.
Take a look at boomer WhatsApp in India. Every single boomer shares stories with images of Gods or daily morning blessings, where they went, what they cooked etc. The network effects are too strong. Nobody wants to miss out on the stories of their grandchildren's birthday or their nephew's marriage.
Even I wish that there was an en-masse migration from WhatsApp to Signal. But that's just a HackerNews pipe dream. Not happening.