As far as I understand, most legal systems before and around the time of the Roman Empire mostly relied on a rescript system.
So legal authorities didn't really research issues and concerns and issue decisions on their own. They waited for a request and then wrote a response for it.
I guess the only problem with relying a whole legal system on this structure is that it's not very efficient. The decrees are very specific to that situation, so it might be more difficult to use these decisions as precedents. The great part about decreeing various general laws is that they are easy to apply.