As cool as repairing other people's gear might be... Wouldn't it get old after a while? lol
It's not like making someone's 3 star gear for them, where maybe you just make them one or a couple pieces in maybe one rare occasion. And with the 3 star armors, only a few of your friends might even spend the time having them made (there are cheaper alternatives that most people do instead).
Repairs is something
EVERYONE needs done at some point and it's something you pretty much need to do daily or at least frequently. So, while there are lots of crafters out there that could do it (just need lvl40), it would make you really busy (since if it seems like a good idea, one would gleefully do it at first to be helpful)... And while, I agree, some people will pay you, most are going to expect it for free. Unless you solicit your crafts often, you don't really see that most people expect to only tip low, if at all. Oh yea, and most would expect you to provide the necessary dark matter, because well: "What do you mean it requires reagents to repair?! Do you have some extra I could use?"
Not to be negative, it's a nice idea, it really is. It just that I'm in no rush to see it changed...

I really don't mind helping people. That's really not what this is about. It's more like people that demand you give to their particular charity, when you have a charity you already like and donate to. Most of us enjoy helping out in the ways we can. Repairing other peoples gear would become sort of a thing like "what do you mean you don't want to do it? are you selfish?" kind of thing, yanno, just after you repaired 100 peoples armor in a row and all you wanted to do is run one dungeon and haven't yet because of all the requests... lol The demand for people that want "help" will be
HUGE and difficult to accommodate.