was there a good reason for a search engine to provide email service? :)
And assuming you mean Google, the question is based on a false premise. They were an advertising company years before gmail was introduced, and an ad-tech company being able to trawl your mail to find ways to advertise at you is a very different proposition to a search company releasing the same product.
much like POSTMAN can trawl through all my API calls to see what other business they make from all this data they are mining now, yes?