It's a much bigger company under much stricter rules and regulations. It's well understood that a small startup will have a much more lax security posture around customer data than the trillion-dollar technology company.
I use GMail with the understanding that Google has access to my activity and content. However, I trust Google to not divulge* my activity and content to other email recipients and senders. That's enough privacy for me in my normal email usage.
* disabling the option of blocking image-loading in the iOS GMail app is definitely an aggravating and inexplicable tactic, to the point I'm starting to looking into switching away from GMail as my provider.