I don't think storage cost is the reason, more that it's hard to design for regional failures. DB by itself as one example, cross region read replica usually introduces eventual consistency to a system that'd otherwise be immediately consistent.
Thanks for the helpful reply! Do you think that would be still true if one accepted a constraint of the "down" version of the property served had data that was stale, say 24 hours behind what the user would have seen had they been logged in?
Yeah except it would probably be delayed way less than 24h. And then you have to figure out how to merge the data back in after, unless you're ok just losing it permanently. And make sure things are handled right if other healthy DBs point to things in the failed-over DB that disappeared.
