Base layer smart contracts contain a host of issues (according to many). The big point is every contract has to be carried by the nodes. Another is security.
With it on a sidechain, it can scale since node operators are not required to house each one and, if there is a hack, it doesnt affect the base chain.
There are some who feel we do need some smart contract on the base layer of Hive. I have a feeling these will be more like Hive Engine where they are not open to the general devleoping public.
I see. Thank you for the explanation, that shed a lot more light to things that I didn't quite understand.