The problem is that the following properties changing values directly influence the success chance
(for armor)Increase in each resist (based on the final value - an enhancement of 4 from 4 to 8 is much less likely to break than from going from 17 to 21).
Increased Luck
Increased Durability
Lower Requirements
(and for weapons, adding elemental damage).
Note that for wood, the top woods increase 18 resists, (compared to 12 for the best leather and 13 for the best ingots - and those don't affect, or barely effect, one of the 5 resists, unlike with wood). It fundamentally has a much higher chance of failure as a result.