So I'm just downloading the latest MacOS security update 2018-001 and it's a whooping 1GB download. Did some web search but couldn't find any explanation why MacOS updates are so big in size. I had a minor point update version a few days ago sized ~2.5G that's almost half the size of the OS download. I don't think any other OS update were ever this sized.

And a minor update taking some 20 minutes to install. Even windows updates are much smaller and faster if I remember correctly. Is this something to do with MacOs apps are designed or it's something else?