I think there're synonyms with different applications in a sentence. Gambling is also understood as betting. The search results showing for each words is gotten from the keywords different sites use in writing about the both words. The classification are best organized to fit into the sentences such as to increase readability. Sport betting sounds better than sport gambling. Yet, both words means similar things. I don't think they mean different things.
Between they're lots of synonyms that can be used to mean same thing. Whenever a person hears of gambling he'd remember or think of betting almost immediately. So the complications are not much, it's just a misconception for too many people. Wager also is a word that can substitute betting. In an ordinary level of reasoning, I'd add that gambling is a broad term for the niche. While betting is the act of spending money in gambling.