The bizzaro logic I see - the average attendance is falling and the arenas aren't used up to their capacity. So let's build even bigger arenas.
It seems like you're missing all the context here. The KHL isn't building average arenas for average teams that will have an average attendance.
SKA is the only club that has both been one of the most attended and most successful teams in the KHL history, and clearly aims to become the most attended team in Eurasia. Building the premier hockey venue is a step towards that. The St. Petersburg pride also plays a huge role, as it's very important for the Northerners to beat Moscow in any way.
Sibir has one of the best crowds in the KHL, and Novosibirsk is the 3rd largest city in Russia, but their 6k-seat stadium has been in use for almost 60 years. I definitely expect average attendance in that arena to increase.
Torpedo and Avtomobilist has been consistently filling the arena for 95%+ for years, I think it's clear that they need to upgrade their 50-60 year old arenas with 5k seats.
Avangard is self-explainatory.
So yes, let's build 'even bigger' arenas.
Now, whether we believe the drop in attendance last season was a reversal of the previous upwards trend or anomaly caused by certain external factors is a matter for the KHL attendance thread. But I see no issue with any of the projects discussed in this thread.