I barely see gambling ads on instagram too but since it's social media it can be used for promotion. But most times I see it on youtube when watching youtube videos and it can be annoying and then if you watch reelshots they have gambling ads a lot but gambling ads on instagram are not much I think they have strict advertising policy against it.
Anti-advertising policies are only to a certain extent, social media accounts and networks are always flooded with such advertisements, once we are curious to search for gambling related information on social media, there will be suggested news and we can see that gambling will continuously appear on what we are watching every day. Even when it comes to just watching sports, gambling site ads can be highly recommended, difficult to prevent, and can only be maintained with awareness rather than requiring social media managers to do more.