That's interesting, I would have thought the opposite -- that it's tandem aircraft where you'd want an ambidextrous stick grip, not side-by-sides.
In the left seat of a side-by-side model, the airplane is flown with the left hand always, so the right hand (presumably the dominant hand) is free for writing and manipulating panel controls. So you can just go with a left-handed stick grip (I have a left-handed grip for the left seat and a right-handed grip for the right seat). That being the case, I see no advantage to an ambidextrous stick grip in the side-by-side, at least no for the left seat.
On the other hand, in a tandem aircraft that is normally flown with the right (dominant) hand, you may want to switch hands occasionally so you can use your right (dominant) hand to write and/or operate controls on the right side of the panel. So that's where an ambidextrous stick grip may be advantageous.
Though in either case, I don't see that as a major concern. If/when you do switch hands, it'll be for just short periods of time, and you generally wouldn't be manipulating any switches on the stick grip during that time. You'd be busy doing something else, whatever it is you're using your dominant hand for.