Above-ground tanks cost less overall than underground tanks. At a later date an above-ground tank can be exchanged for one of a different size. Above-ground tanks take up space and are visible to the neighbours.
Underground tanks are more discreet: once installed in the ground only a shaft cover remains visible. For that reason they tend to receive planning permission more readily than above-ground tanks. Exchanging the tank or decommissioning it at a later date is very expensive.