Me too. It's obvious that the two permanently coupled cars are really just one big car with a toilet, and it's obvious from the start that they should just have put a toilet in every car. But that's too easy to be the point, I suppose?

Maybe it is a parable against yet another workaround?

Having two permanently coupled cars is obvious.

It is NOT obvious that they should have put a toilet in every car. The solution works quite well and you save a potentially large amount of money.

But then they could have just build bigger cars to begin with, which would have been even more efficient?

That would affect turning radius, and what tracks the train could run on.

Unless of course you built them like the large buses with a swivel in the middle, but then you get into non-standard stuff.