Why very short peptides (dipeptide and tripeptide) are more expensive to synthesize than those with regular length?

For very short peptides such as dipeptides or tripeptides, solid-phase synthesis is not applicable due to the length. We need to use the liquid-phase synthesis method, of which the cost will be a little higher than solid-phase synthesis.

Other than dipeptides and tripeptides, the synthesis will be stick to solid-phase methods.