I sincerely hope this* wasn't an epiphany for anyone here.I think in reading the Groups.io announcement it can fairly be inferred that in Mark's view making money is necessary in support of developing and supplying the service, not the other way around.
Which is a distinction Jeremy had pointed out:
Faced with that, I think what Mark is most interested in is finding a pricing scheme that is effective, acceptable to the payers, and consistent with his view of what groups are for.
This is largely a practical question, and Mark's view has evolved over time. From the first Mark expressed a preference to avoid reliance on advertising, but in the very early discussions in beta it was proposed that Basic groups would be ad-supported and Premium groups remove the ads, increase capacity, and add features.
It wasn't much later that investigation and introspection convinced Mark that using advertising was an unappealing prospect, for several reasons, and so it was taken off the table without ever having been implemented.
*Referring to Samuel's comment:
I think we can be clear that the purpose of Groups.io is to make money