Google absolutely had a cohesive messaging app (Google Chat, later called Hangouts), they just threw it away and tried to rebuild it several times and under various other names and paradigms rather than iterating on it.
If they'd simply added a "WhatsApp/iMessage mode" to Google Chat in 2015 (i.e. allow Google account based users to seamlessly communicate with phone number based users), I think we might be seeing a very different messaging landscape today.