If you choose Native ads, likely you will not using the normal banners or other types. separate this will cause the sdk size small.
The team is investigating ways of using proguard to strip unused methods to decrease the build size on compile for Android.
There are also situations where publishers use both native ads and other ad formats.
We are constantly looking at ways to decrease build size for both Android and iOS without causing confusion to our publishers with multiple SDKs for a single OS. Splitting the SDK up into multiple SDKs would cause difficulty if the ad formats the pub is looking to use is not included in the SDK their are downloading. as the permutation of 3 ad formats (banner, interstitial, native) yields 6, it doesn’t make sense to have 6 SDKs. This is why we have one with all ad formats despite the minor increase in file size.