Not to mention that they allow for better space utilization. Direct Attached Storage (DAS) is very wasteful of disk space that cannot be reclaimed because it is locked to a specific host.
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There are two issues with this statement:
1) Talking about VM-centric storage that is hyper-converged (storage virtualization stack co-exists with a hypervisor on the same hardware) storage SHOULD be as close to host as possible. To allow shorter I/O path and better performance. Distributing all the data between nodes is possible (some Virtual SANs do this and others don't...) but that's not optimal in terms of performance.
2) "Storage is locked". Not really true. As stated in 1) quite a lot of Virtual SANs do so-called "wide striping" (Erasure Codes, network RAID5/6 etc) and slice data between the nodes. So nothing is locked,...