In every account I can find it is mentioned that a dullahan fears gold, even in as small a quantity as a pin, but why?

Every source labels it as an 'irrational fear', suggesting that it does not actually physically harm a dullahan, or it would be a 'rational fear'

In my own research (which is by no means source checked or professionally conducted), the symbolic meaning of gold as a material was that it was associated with the sun, as opposed to silver, representative of the moon. This makes some sense, however I can find no source dictating that dullahans are unable to ride during the day, only that it is equatable to personal preference, dullahans choose to ride at night because they prefer to remain unseen.

The reason this vexes me, and strikes my curiosity, is that gold is commonly associated with death in MANY cultures, especially in Europe, the most obvious example being Charon, who demanded gold as passage over the river Styx. In addition, the Roman name for the greek god of death, Pluto, was derived from the greek word for "Wealth", and was also referred to as the "Rich Father". In addition, it is well referenced that, as ruler of the underworld, Hades/Pluto had a plethora of riches. Other cultures, such as Egypt, the Vikings, and many MANY more have tied gold to death. So why is it then that the Irish embodiment of death fears the material most associated with its own affiliation? I would appreciate sources in the discussion pls ;)