I'd wager that there is some connection to the direct democracy thing: once you'd have any sizeable party in opposition they could abuse the referendum system t

I'd wager that there is some connection to the direct democracy thing: once you'd have any sizeable party in opposition they could abuse the referendum system to bring the legislative process to a near standstill. It might be not the only reason for the way the executive branch is set up, but IMO it's an important part of the system as it is.