Pay attention to WhatsApp's wording (all privacy/security claims start with "your messages"), and their privacy policy, and you'll see that while message involving with individuals (non-Business users) are secured, your contact list is not, neither are chats with businesses or the metadata about you chatting (destinations, frequency, time)
I encourage you to read the article, but Signal minimizes the metadata it stores about you, doesn't hold on to you contact list, doesn't keep information about your IP address, etc.
WhatsApp instead makes tons of money from this kind of metadata.
