>More likely that they were well-packaged on the wreck and have only just been released ?

No not at all. Embedded in sediment would preserve them better.

Like bog shoes?

The leather on those shoes are in nearly perfect condition! How can that be possible??

Likely anoxic or anaerobic conditions where nothing decomposes. It isn’t that uncommon in nature.

Leather can survive for surprisingly long time in anoxic environment. E.g. in a swamp.

Not only for a surprisingly long time, but also in surprisingly good condition. For example at Vindolanda on Hadrian's Wall archeologists have found not one or two, or even ten but over 5000 amazingly preserved Roman shoes that were apparently thrown away into the fortress's moat and survived buried in the mud <https://www.vindolanda.com/Blog/the-curators-favourite-shoes>.

Hilariously they're never found a pair of shoes, only singles. So that's why they think they were thrown away as rubbish, because one shoe broke so they threw it in the ditch. In the museum on site there's a fantastic "wall of shoes" on display where you can see the amazing leatherwork from 2000 years ago <https://www.thehistoryblog.com/archives/37305>.

> Hilariously they're never found a pair of shoes, only singles.

From that first link: “These two little treasures were part of the hoard of over 400 shoes excavated in 2016. One would probably think that we have lots of pairs of shoes however, we only have a few. But this pair was easier to identify as they were small and have a less usual construction style as they do not have a seam that stitches them up over the toe and they were also found close together.”

Also, looking at those shoes, many of them don’t look beyond repair to me. Quite a few look like they’d need only minor repairs.

My prior understanding was that before the industrial revolution dramatically reduced the labor costs, clothing was expensive. Most people only owned two or three outfits, and replacing one would cost a month's wages sort of expensive.

How could one afford to throw away a perfectly good non-matching shoe?

they threw away the broken one after replacing it with a new one. they didn't replace the good one.

when shoes are hand made it makes sense to not make them only in pairs if only one shoe is needed

Why not fix the broken one?

Sometimes the Cobbler tells you it's too far gone.

Looking at those mesh-like patters in the shoes, makes me wonder how long each one took to be made.

*pairs of shoes were very rare, not nonexistent

I wouldn’t call those near perfect. Parts have clearly rotted away.