Shanidar Z — The 75,000-Year-Old Neanderthal Woman Whose Crushed Skull Was Rebuilt From More Than 200 Pieces
The short honest answer is that we do not know precisely.
Some ochre at Neanderthal sites appears in association with stone tools and may have been used for practical purposes — certain forms of ochre can be used to bind adhesives, which would be useful for hafting stone tools to wooden handles.
This is a functional explanation that does not require symbolic cognition.
But ochre has also been found in contexts that are harder to explain purely functionally.
At sites like Maastricht-Belvédère in the Netherlands, ochre was present without obvious practical correlates.