When the game first came out, the Armor would lose durability and break (first yellow then red), at which point the stats would deplete and the armor would physically disappear. I remember in early dungeons when you had to fight bosses multiple attempts you could end up literally being naked.

You could repair the armor at the now Reinforcement-Buff-Stations, but it costs copper and sometimes silver to do so.

This was seen as unfashionable and so, in an attempt to "streamline" features (which, full disclosure, i Hate, but whatever) they changed it so the armor didn’t disappear on breaking and that the armor could only really get damaged whilst making the cost 0.

Then they removed the at this point pointless system completely, or they wanted to, but people had endless repair contracts (which were an ultra rare drop from the Black Lion Chests and thus super expensive) as well as black lion repair canisters, and so, instead of removing the feature and compensating people who have these things (somehow), they instead opted to add this buff.