What PG calls "bets" I would call interesting topics for Newton. Maybe he just liked the subjects. Calling bets is saying he was trying to actually accomplish something out of their studies and work. I don't think a curious mind would work like that. Even in physics, he studied a broad range of topics, not only Mechanics.

Furthermore, you don't need to make a breakthrough in everything to satisfy your desire for knowledge. Even more so for Newton, which was known by his seclusion and introversion.