And that's to do with the looms. Thing is - if you want to sell cheap fabrics, you need to have a loom that is fast, and work with materials that don't have a life of their own. Which means limp yarns, not spun as tightly old-fashioned hand-spun ones, in
a loom that is really, really fast... and these things will not give you proper selvedges.
If you want a fabric that meets all the criteria of a historical fabric, you have to have a good old-fashioned selvedge like that. Which also explains why I'm always happy to get something like this:
That is a proper, nice selvedge; a little bit stronger than the rest of the fabric but not too different in weave or density, and there's no plastic strengthening thread added to it. You can join two of these selvedges with overcast stitch just like it was done back in the Middle Ages and be happy.
The next best thing, and a type of selvedge more commonly found in modern fabrics, is looking like this:
It's still a proper selvedge, though not as nice and sturdy, and quite wide if you don't want to have the change in weave type show on the surface. There's also often a messy-looking area between the weave proper and the selvedge, also nicely showing in this specimen here. I wouldn't join two of these with overcast stitch if the join will be visible later.
Now let's go a bit more modern, yes? Proper selvedges require shuttle looms. These old-fashioned shuttle looms are slow, and modern industry likes its stuff to be faster - time is money and so on. So there's another type of fabric edge which really can't be termed "selvedge" any more... this one.
These are done with help of jets or projectiles, requiring cut threads as the weft. These weft threads, if fine enough, can be even carried by an air jet or a water jet. The result? A very, very fast loom (these are the fastest type today) but no selvedge whatsoever. The edges are, basically, cut edges with a little fringe and maybe some stabiliser thread along the edge. If you wanted to use the selvedge for extra strength somewhere... you're out of luck with this fabric type. If you wanted it to show somewhere... same thing applies. If you were planning to cut down on your sewing and hemming time with use of the selvedge, you just got a nasty surprise. You will have to treat every edge of this fabric like a cut edge, because that is what it is.
And then there's another little nasty surprise if you are looking for pure wool fabric in narrow widths. One of the two edges is a perfectly fine, normal selvedge, usually not reinforced by a double thread or anything.
The other edge, however... is not a proper selvedge. In fact, it's more like one of the cut-thread edges, only with a fold in the thread instead of the cut. The edge is held together by a fine, tiny crochet chain, usually done with a very fine thread made from man-made fibre.
It's not very obvious, and won't be visible or noticeable to most people, but it's not acceptable in case you want to have an as-authentic-as-possible equipment. If you remove the chain, you also remove the structural integrity of that edge.
If you want to have a pure wool band without that chain, though, you can take a sufficient length of the weft thread, a needle with a blunt tip and a large enough eye, remove the crochet chain and thread the extra thread through each of the edge loops. It might be advisable to remove the outermost warp thread for that, and to stock up on enough chocolate and motivation-enhancing drinks before.
Fun. Right? Thank goodness there are still some old-fashioned shuttle looms running!