Well, if you're targeting the display network, or uploaded a video ad, it's natural for the ads to go under review since Google has to make sure your ads comply with the rules of the countries you target, each country. However, if you're targeting the search network, it means something in your account looks fishy to Google hence they are reviewing it each time. Now, if your account did raise a red flag, for some reason, every change you make in your account, like: budget, ad copy, adding keywords etc will make it under review again. If your account is indeed fishy, you're about to get banned
