I work in the game industry and I can say that 90% of decisions related to size and materials are based on:
1. What did we do before?
2. Is there a standard size for production?
3. Premium shelf space (box size)
4.. If we do something different then how much more will it cost.
Ish is right that these table numbers are based on multiples of the killteam cardboard board, which is also a standard size paper for UK.
I also think that players will keep playing in whatever they already have because players often use the same logic as above.