For massive amounts of high-performance storage, the cloud is absolutely the most expensive option, by far. Even just 100+TB is ridiculously expensive on any cloud provider. If your company revolves around large amounts of data, it can make sense to keep it on-prem...

...but only if you compute the TCO. The bandwidth, peering, service contracts, available power, cooling, networking, rack capacity, half-decent smart hands, spare gear, etc, etc. The disks won't be the majority of your bill, and the logistics are difficult. It can still be cheaper than $CLOUD, but you have to deal with all the cost and complexity that comes with DIY, so do your homework first.