All named instances are not included in variable font

My designspace file contains many named instances in the format of
```








```

etc
But when I generate a font by command.

`fontmake -m Myfont.designspace -o variable`

only the default instance is added as named instances.
How to include all the instances defined in designspace as named instances in the font ?

Reproduce the issue with the provided designspace structure and the command `fontmake -m Myfont.designspace -o variable`. Inspect the generated variable font's named instances and compare them with the instances declared in the designspace; done means all defined instances are included.

Written by the indexing model from the issue text.