Are you saying that these pilots were not trained in how to deal with IIMC?,
More that the recency of that training has a big effect - instrument flying is a perishable skill, it has been said on here many times before.
Many pilots prepare for a planned instrument flight diligently but far fewer are ready for when an anticipated or intended VFR flight suddenly switches to IFR.
The quality and recency of your training allows to you 'switch on' your IF head and concentrate on the AI.
I've been flying for 39 years and your first time in cloud for a while can still unsettle you for a few minutes as your brain struggles with the lack of visual cues - that is where the training kicks in.
I still challenge myself and often fly IMC with no AP just to keep my skills sharp - even then I can make errors and get the 'leans'.
What chance do you have if you never see cloud, never practice an IMC abort for real and never prepare a plan B for IMC just in case when the weather is poor - that is reflected in the accidents we keep seeing.