If you have root access, you can browse /data/app
and that's the difference.
# Sample for Android K 4.4
com.android.vending-1.apk
com.google.android.apps.maps-1.apk
# Sample for Android L 5.0/5.1
com.android.vending-1/
com.google.android.apps.maps-1/
And if you list the content of one of them, you'll see
com.google.android.apps.maps-1/:
base.apk (54MB)
lib/
com.google.android.apps.maps-1/lib/:
arm64/
com.google.android.apps.maps-1/lib/arm64/:
libcronet.59.0.3602.4.so
(4.9MB)
libgmm-jni.so
(9.4MB)
Also, Android 4.4 implements the old Dalvik VM, while on Android 5+, Google switched to a new VM called ART. The main difference is that Dalvik compiles apps Just-In-Time (JIT), while ART compiles Ahead-Of-Time (AOT), so more code is compiled in ART than in Dalvik. That's why this one is really big:
/data/dalvik-cache/arm64/data@[email protected]@[email protected]
(109.5MB)
On Android 4.4 it's much smaller, you can find it out by yourself.