Ads between levels are a common practice and they are a great way to keep the app free to play.
We understand why you do not like the ad feature but with all its downsides it is a perfect opportunity to let you play the game for free.
If you don't want to see the ads between levels you can turn them off by making NoAds purchase in the shop. Some purchases include permanent NoAds feature, while the other disable ads for a specified period.
Please note that, the rewarded offers like 'Extra time', 'Free booster' and others will still be available to you, so that you can keep getting extra resources! Such ads are not disabled by the NoAds purchase.
Thank you for understanding!