>>95974516Encouragement and mindwashing from GW mostly, that this is the only proper way to play;.
>Buy latest product.>Play with latest product in the shop/showroom/tournament = you become a free advert for the product to other potential customers.They don't want you using non GW parts or scratchbuilds because THEY DON'T SELL THEM.
What you do in the privacy of your own home is your own business, scratchbuild and proxy as you like, but most GW players don't get this - many have only ever played GW games and think this is the only correct way to play a game, so freak out when they see someone not playing by the rules they have been taught.
Other factors are Sunk Cost fallacy, mindless Brand Loyalty and GWs expoitation of those with poor reasoning and impulse control.