Because most endo's, I'd say all endo's never prescribe high levels of estrogens and
don't understand its effects and you said it yourself, 20-30 years in the business,
there wasn't any HRT prescribed and little study on its effects 20 years ago!
Doctors who just came out of school (or internship) would have a much more modern
view and knowledge of this. Most doctors don't fully keep up to date
as much as they should.
Clotting caused by estrogen comes from byproduct of its
elimination from the blood in the liver that flows in the blood
and promotes clotting. Its not that progressive,
it can caused clotting and blockage pretty quickly.
The other type of clotting is a byproduct of atherosclerosis, deposits in the arteries
very slowly block the arteries and sometimes they detach themselves blocking smaller
arteries that feed the brain (strokes), or another tissues (heart or another muscles) causing
partial or total tissue death.
Aspirin helps with the second type of clotting, not the first.
Though, if you've already have partially blocked veins and arteries of the
second type, then you would be more highly susceptible to blockage of
the first type.