I see this question once a month. TLDR they're a juge company and it's a result of PMs building a product and leaving and sometimes products get killed (see Google's Graveyard: https://killedbygoogle.com/).
The multiple apps started out in different segments and areas (mobile, web, enterprise, consumer, etc).
https://www.quora.com/Why-does-Google-have-so-many-messaging...