Fair question. For me, it's because every time I trade a vehicle I incur some monetary costs, some costs with my time, and it means my next vehicle trade will be at least 2 more years away. So if I traded my Gen 2 for a Gen 3 I wouldn't incur nearly as much monetary cost. Granted. But the time cost to me is still there. I have to deal with dealers, close the loan on my Gen 2, open a new loan on a Gen 3 (I don't have to finance, but I choose to because I find it financially smart to do so--YMMV), and then I've got some Gen 2 mods, so do I transfer them over? So there's a large time cost.
But the main thing is, I'd rather hang out a year and see what the Raptor R offers. And after I see that, I might choose a TRX instead. I don't want to be trading vehicles every 12 months. Even if the cost of trading is low, for a luxury item that does cost money to changeover, I'd rather prioritize that money for other things for my family.
So I've had my Gen 2 for 18 months. I'm gonna hang onto it another 9-12 months and see what the market has to offer. At that point I might still stick with it, or I might got for a R or a TRX. Just don't know. But if I got Gen 3 now, I kinda push myself out of having that flexibility in 9-12 months.