Materia and gear breakage as it is runs the flow of the game. Crafters always have things to make because people are always breaking / melding gear.

If you give us "Safe slots" the market will become oversaturated in a matter of moments. FFXI had this issue even with materials being painfull to gather for the best gear the result?

NQ gear became useless and HQ gear shot in price insanely high to make any kind of profit.