There are a lot of things I'd love gmail to do for me: filter for passive-aggressive turns of phrase, remove people from party invites that I am going to regret having included later, auto-link relevant GIFs on certain key words. But this particular issue -- uncertainty as to who to include on an e-mail -- is not one I've ever felt impeded my e-mail efficiency or believed would benefit from a "helpful hand."
Sure, you could argue that having suggested contacts there "could come in handy" or something, but I'd argue, if anything, their inclusion adds time to your e-mailing process, either because it sends you down a tunnel of nostalgia ("Oh, yeah, I remember when I used to include Tim on these group e-mails....") or because it makes you feel more guilty about any sort of sketchy social maneuver you're pulling (i.e. consciously excluding Daisy from brunch while her name sits right there glaring at you).
Also, who wants to feel that their internet conduct is that predictable? Gmail, you've homogenized enough about how we interact/communicate -- give us at least the illusion of autonomy!