Because most japanese fans I know are disappointed but understanding, and leave it at that. A lot of them outright mock the absurd behavior of those spamming the national dex all over twitter, and think that foreigners are being way too petty over the situation. They seem to hope for the best and hope for their favorites to get in, but they aren't going to constantly pester Game Freak about it as it's rude and not worth it.
Honestly, I 100% agree. I've been very vocal about frustrations with GF since like 2014, but as of late I've been not nearly as uptight since SM proved they can still make very fun games, and the real thing that bugs me lately is the annual release schedule and the hellish crunch they go through. USUM has no reason to exist and didn't even fix the issues that SM did have, and LGPE was pretty pointless as well and failed to add anything to make it the definitive Kanto experience. SWS look promising and I'm personally hoping they're focusing more dev time on post-game content like a battle facility or second quest if they're cutting pokemon, but I was also mad to hear about the dex cuts.
Still, people have been going WAY too far over this to the point even I can't take them seriously anymore, especially with them nitpicking fucking trees and water now. The fact people act as if ORAS's dumbing down was a thing everyone was mad about for years is just sad since I was pissed from day one of that horrible game, yet all the fanbase did was make stupid excuses for why it lacked Emerald content. But now that the national dex is removed suddenly it's a serious, important and bad turning point in the series history? Five years too late, I say... So yeah, I don't really take the fanbase seriously anymore and I think Japan really doesn't either, which is why I'm amused to see people on twitter make up a japanese hashtag only for hardly any Japanese to use it