Alternate multi-user pricing model?

I’m evaluating Zeitkapsl for sharing family photos. In that scenario, storage requirements would be relatively low (the 50GB tier would likely be sufficient pretty much forever), but I would like to share albums with several people, some of which should probably have write access (see my other question). When you only need a fraction of the capacity, the “extended” tier feels pretty expensive though, and >5 users isn’t even an option.

Out of curiosity: Is there a technical reason for tying the price to the user count, or is that just an additional, mostly arbitrary point of separation between the tiers?

(Apologies for barging in and immediately questioning your product pricing! 😅)