Because you need the updated rules to play anywhere other than in your own private games? Yeah, ‘dont buy it’ also means, ‘play it in a limited fashion’ as well. So there’s always that aspect. There was this same debate regarding ADnD back in the day – everyone wanted to remain on 2nd Edition rules, but you couldn’t go to any conventions and play, nor were you getting any new materials.
There’s also the fact that if you want to increase your army, you’re kinda stuck buying their stuff.
This is almost like telling people “dont buy gas then” when they complain about how much the costs rise. Sure, but then how will I drive my car?
The only thing I can see that they stupidly do is continue to purchase GW paints and paint supplies, when they are easily 3-4x the cost of other (imho much better) options. The only reason I can see there is simplicity, since GW paints are coded so you can apply the same colors as seen in their graphics, which probably appeals to the less artistic-minded gamers.