Types from attrs.define classes not shown in description

Say I have an attrs class, e.g.:

import attrs

@attrs.define
class MyClass:
    """
    A class that does something.

    Parameters
    ---------
    a
        The parameter a
    """

    a: float = attrs.field()

Then in my conf.py I have added "sphinx.ext.autodoc" to the extensions list, and set autodoc_typehints = 'description'. I expect that in the generated API docs that the parameter "a" should get the type "float" added to its description, but I don't.

My actual repo (pointing to a PR where Ive added autoapi): https://github.com/21cmfast/21cmFAST/pull/575
A specific class showing this behaviour: https://github.com/21cmfast/21cmFAST/blob/b0eaa28630f8da31e889fa1badad6892732a4718/src/py21cmfast/wrapper/inputs.py#L1448
The generated docs for this class: https://21cmfast--575.org.readthedocs.build/en/575/

Start with the attrs.define example and the conf.py setting autodoc_typehints = 'description', then compare the generated documentation for the linked inputs.py class. Trace how sphinx.ext.autodoc handles the parameter description and verify that the generated API docs include the float type for parameter a.