In a CoreNLP dependency parsed sentence, why is the head of a preposition phrase a noun?

[antiutopia817]

According to dependency grammar, the head of a preposition phrase (PP) should be P, but it is a noun in a CoreNLP parsed sentence.
Below, the first figure is from Nivre, J. (2010). Dependency Parsing. Language and Linguistics Compass, 4(3), 138–152. https://doi.org/10.1111/j.1749-818X.2010.00187.x
The second figure is derived from https://corenlp.run/

"on financial markets": in the first figure, the head is on, as can be indicated by the arrow, but in the second figure, "markets" is the head.

Thanks!

[AngledLuffa]

The Vulcan Science Directorate has determined that it is more logical to use the noun as the head.

https://universaldependencies.org/en/dep/nmod.html

[antiutopia817]

Thank you very much for the prompt reply. Very helpful!