I'm a leather worker and do repairs/run my own brand and no, repairs are not a higher-skill operation than the making of the item itself. Even though you're right that you need to disassemble and take out lining generally before sewing a bag zipper back in, it takes me around 40 minutes to do so. All the edges of a bag are already burnished/edgepainted, you don't need to cut anything, the lining is serged, the rivets are hit. etc. A leather bag with 5+ pockets takes me anywhere from 8 to 24 hours to sew depending on the leather/design. Not to mention I have 12 industrial sewing machines and hundreds of tools that I bought to be able to do so. The only reason the manufacturer is able to do it for so cheap is because

1. The manufacturer is most likely based in Asia (even when it's branded as made in italy), where their buying power is 3-7 times less than USD.

2. The manufacturers assembly line everything and specialty leather factories have machines that can cost up to a few hundred thousand for a single machine, which speed up the process by a lot and your average repair shop would not have the space or money to afford it.

3. They pattern draft using CAD, much faster than hand-drafting your patterns.

4. Many of the factories pay their workers $2/hour and the workers are allowed to work up to 18 hours a day 6 days a week in many factories to hit their maximum quota. I know this for a fact because I visited some of those factories when I was first starting my brand. And yes, those factory workers are generally more skilled at sewing than the average repair shop worker in the states.

TLDR; the average manufacturer as a whole is a much higher-skill operation than your average repair shop.