Why is the gain of this amplifier so small?
In your calculation, you have made an error.
It is correct that the gain is determined by ro||RD||Rload - however, in this expression the quantity ro is the small-signal output resistance of the FET (equivalent to the inverse slope of the Id=f(VDS) curves, normally in the higher kOhm range). Hence it is wrong to use the DC values for calculating ro (VA/ID, resulting in a very small value).