Why is Hopkins getting away with his holding and hitting style?

[chito]

I saw again his 2001 fight with Felix Trinidad and I noticed this style of his which made me question… did the referee never tried to give him warning for doing this? I never hated Hopkins in fact I admire his power and his ring wizardry but this style of his which I call "magulang or madanyo" [pardon me for using my native tongue for this] is very effective most of the time especially during the fight with Trinidad.