I don't know why unless it is to repair vintage clothing or they don't know any better. The seller is selling it cheap to get rid of it and someone will think it's a good deal but it's not. Where thread is concerned you only get what you pay for.

Your teacher was right. Old thread like old clothing is very fragile

Save your money and buy good new thread when it's on sale. There is nothing more frustrating that trying to sew with cheap or old thread that twists and breaks all the time

That does make sense for vintage clothing if you want to keep everything authentic.

Some people collect the wooden spools.

I've been sewing for 45 years. My mom passed in 1984 and her thread collection (large and varied) came to me. I am still using some of those threads today. I have NEVER had a thread failure. While there are certainly possibilities that "natural" threads such as silk, cotton and rayon may break down, I feel as if the risk is sometimes exaggerated. If thread is stored in a reasonably stable environment, it may be good for a very long time. I've heard that refrigerating thread prolongs its life, but as a person with a solid science background, I can't understand how that would be. I feel connected to mom when I use one of her ugly colored 70s thread for a craft project or machine basting. Getting thread for a low price on eBay will probably work out. JMHO.

KathyinJax

I inherited a lot of thread when a family member passed away a couple yrs ago. The better brands were fine, cheapo/no-name types, mostly all dry rotted. They broke with a gentle tug....
I wouldn't even baste with it, tossed the cheapos out. They were all less than 20 yrs old. Kept the Gutterman & Mettler, they were all fine.

Now if they were really old, or on pretty spools, they could be used for decorating in the sewing room. A friend of mine has some very cute vintage sewing pattern/threads/notions in her sewing room on a shelf over her machine.

It seems like cheap thread that breaks when it is new is not improved by age. But quality thread is better if you are buying it old. I hate thread that has little lumps that make the machine stop at that point and you have to stop and rethread.

FWIW, there are a number of crafters using colorful spools of vintage threads to make other items like picture frames, jewelry, etc....

& also FWIW, I also am the lucky owner of a couple of drawersful of vintage silk, nylon & cotton threads from decades past, inherited from my great-aunts, & while I occasionally find 1 that has perished, most are still in fine condition.

When it comes to "vintage thread" it translates to dry rotten thread. NO way I'd use that stuff for sewing. Not even on vintage clothing. Most would buy it for crafts using the wooden spools

I saw a lot of empty wooden spools on ebay without bids, but a lot of thread with bids on wooden spools.