Increasing safety margins...
Especially maybe on non-dry runways when friction coefficients are not accurately determined...
Separately, some operators do not maybe want to operate on the limit of V1 for each departure, especially when a decision delay of a fraction of time could be the difference between stopping as per AFM and disaster in case of eg a cliff at end of threshold... To each operator the choice what to do.
IMHO, depending on the operator, their crew training and average/minimum crew experience levels it would be wise to have an artificially lowered V1 for these reasons. Increasing safety margins by reducing V1 would surely be on the forefront of my mind in certain types of operations.