One strong reason is that the data needs to be shared across hospitals so that you are not locked into one institute. It doesn't make sense for different hospitals to duplicate your data on their servers for cost issues.
Also the data really kinda belongs to the patient so perhaps the patient should be the one paying for the archive of the DNA sequencing.
Alternatively, service providers may wish to analyse your data and offer to store it for u in a sort of a barter trade ( Your DNA/ disease status for my mega analysis and in return i store it for u for 'free')
Dell has sold 1M webscale servers in five years