How are you providing network level redundancy with dumb switches? My only guess is that the ISP is already doing HSRP/VRRP on the gateway and you can setup multiple NICs/switches with something like CARP and being careful not to make L2 loops.
Having the handicap of needing to wait 3-4 hours before being able to access your backups in an emergency, could make a day-and-night difference for continuity.
So I would argue it has nothing to do with "being a backup service", but rather that their users could afford a 3-4 hours of waiting. Or that they don't think like that.