When 3.0 released the GMs decided that any skill buff would be 1 slot, and given that offhand exists and could technically allow multiple melee weapon buffs to be used in conjunction, made us go with the current design approach.
On a more technical level... there is a soft limit to how much "stuff" can be going on with a character at a time. Applying all the weapon buffs to you simultaneously is resource intensive and we've prefer to avoid it. This is why 2.0 dragon didn't even try to buff the actual skills.. it did some other stuff that was bad and broken :(
This is also I will be trying to brainstorm on in the near future.
"I have no data yet. It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories instead of theories to suit facts."
- Sir Arthur Conan Doyle, Sherlock Holmes