'Nombreuses' but not 'beaucoup' ?

Question

In the two optional answers below, why hasn't 'beaucoup' been given as an option to 'nombreuses'?Thank You 
Crois-moi, c'est le résultat de nombreuses années de pratique

Crois-moi, c'est le résultat de nombreuses années d’entraînement

Accepted Answer

Hi Stewart, 
The expression 'de nombreuses' used here is just better French.
Take a look at the following lesson exploring the different ways to express quantities -
Expressing quantities in French with quelques/plusieurs/de nombreux = A few/several/many
Bonne Continuation !

Answer

Stewart, I agree with Cécile that ‘de nombreuses’ is a more specific fit, but just to confirm that it is not at all unheard of to have native French speakers use ‘beaucoup de…’ or ‘trop de… ’ in everyday speech in a context like this, so I wouldn’t sweat it too much. See the definitions from Robert, for example :

https://dictionnaire.lerobert.com/definition/beaucoup