Why are contraction joints in concrete pavement normally designed to be unsealed?

For unreinforced concrete pavement, the contraction joint is an approximately 3mm wide groove with a depth of about one-third to one-fourth of slab thickness and a regular spacing of normally 5m. The grooves are designed such that they are too narrow for stones to fall into when the cracks are open due to the contraction of concrete. The groove location is a plane of weakness and the groove acts as a potential crack-inducing device where any potential cracks due to shrinkage and thermal contraction may form will be confined to the base of the groove. It will not cause any unpleasant visual appearance on the exposed surface of unreinforced concrete pavement.

The above-mentioned contraction joints can be designed as unsealed. These grooves are very narrow so that stones can hardly get into these grooves even when the joint undergoes contraction. The fine particles or grit entering into the groove are likely to be sucked out by the passing vehicles. The joints can be self-cleansing and it may not be necessary to seal the joints for fear of attracting the accumulation of rubbish and dirt

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.