If HSEL is of type logic, it can only have a value of 1, 0, x, or z which would explain your problem - i.e. that is why you only see a value of 1 sampled by the covergroup.
But, for instance, if HSEL is of type logic[3:0] then it could take the range of values you are trying to sample only if the bits are not in an unknown state (4’b0001, 4’b0010, 4’b0100, 4’b1000).