Because it is by Yamato, nuff said
I think size matters. If you take 1/60 VF-1 then they are similar priced since they are similar sized. And demand/volume also plays up, certainly there are a lot more TF fan than Macross fan.
I myself wouldn't buy a Yamato at RRP, but at 40% then I might be tempted (got myself a SV-51 for US$80 from YJA, now that much more reasonable)