Maybe because aspirin, which i grew up with and still is my painkiller of choice as well being a bit of wonderdrug IMO has fallen massively from grace and is frowned on it seems to me by everyone in the medical world. I take no notice.
The same question was asked on a TV programme a few days ago. General consensus seems to be an outright no, Aspirin should not be used as a blood thinner prior to the AZ vax.