There are two reasons. First, each well is specifically designed at construction for a distinct range of withdrawal, based upon the size of the well itself and the aquifer formation it is sited in. Substantially bigger pumps would not fit within the well casing. Also, “better” equipment, if it were to withdraw water beyond a critical threshold amount, could permanently damage the well formation.
Second, higher withdrawals from wells would require a permit from Rhode Island Department of Environmental Management, and the agency has clearly stated they would not support increased withdrawals because of the stress on the aquatic habitat in the area due to drinking water withdrawals.