To be fair here, they actually do care about balance to an extent and have tried to tweak things here and there. For Gen 6 and 7 they buffed a few Pokémon's stats like Scolipede and Krookodile while also giving the former a much better HA. Conversely, they nerfed a few abilities such as Mega Kangaskan's Parental Bond, all of the -ate abilities (they only give a 20% boost) and perhaps more infamously, Gales Wings. The weather abilities were also majorly nerfed, which any single format player appreciated after what happened with the weather wars.
The issue comes down to three things: 1) They really only balance for Doubles, so if you play any other format you're kind of out of luck 2) Even with the buffs and nerfs in mind, only very few have moved the meter much in the competitive format. So while you do get cases like Talonflame going down while Scolipede rose up, you often still get Pokémon that stay within their tier with little movement. Finally, 3) they introduce a large number of new variables to balance for such as Z-Moves and new Pokémon that the metagame becomes imbalanced again in a different way. So it's not a case of not caring, it's a case of trying to juggle too many things while only focusing on a specific format that not everyone plays.
It's been stated before, but it's not an easy copy/paste job as many would try to tell you. Strong Bad made
two posts on the matter before, but to get to the gist of it: You can never future-proof models and there will always be a large amount of work that goes into bringing those models forward into the next game on a new system.
Now whether GF is conveying this problem properly in their PR or how it's being reflected in the trailers and gameplay, that's another issue and I have my complaints on the former in particular, but the workload issue is probably something that is legitimate based on what's been said by those familiar with game development.