I added a new attribute with
Default Value set to
I added the attribute to my attribute set and edited the product, but it is set to
No by default.
How can I fix it?
This is not a bug. It's a feature.
The default values serves as "default" from now on. It is not added to products existing prior to setting this default value.
If you create a new product, you should see the "yes" value selected.
There is no "out of the box" way of setting the default value to existing products.