1. It makes more sense than suddenly increasing own craft skill upon entering a building.
2. Adds more value to stable clans as opposed to 1-hour clans (that's how long it takes to build a farm, which can be used for craftng too

Or the requirement may be extended to the building, not shifted. But if shifted, the responsibility will lie on the clan, along with the capacity to be generous to low-levels.
Also, this may depend on player rank in clan: Member can craft 100-199, Marshal - 200-299, Lord - 300+.