Many regulations touch on data flows or storage. If there is any kind of breach, even one from a vendor that stores some of your data, your company could face regulatory scrutiny, among other complications.
Storing data in unknown and unvetted places may result violations or a range of other damaging regulatory consequences if audited.
Likewise, some clients may have regulatory flow-down requirements that require you, their vendor, to maintain compliance. Violations by SaaS vendors could not only impact compliance, but client relationships and bottom-line revenue.