Change = Fear
Also, people are invested in their old sim that they’ve spent years and hundreds/thousands of dollars on - so they want to defend their choice and look more old skoool hardcore than the “Xbox kiddies” here 
They’ll all be on MSFS in 2 years anyways and will have forgotten about P3D… Except those 3 guys still on FS2004 because “it runs just fine on their PC”. 