In most cases, we see delays because the team wants to prolong the time needed for further development, they do not want to just list a coin without any progress in roadmap because it would mean, that they fail to deliver product and this will cause a drop in value immediately after listing.
Basically, when they have a strong vision and they would always put exchange site as an important thing too, you should remember when the product didn't get any demand and it will be another failed product. We must aware they can do the promotion through the exchange listing too. Further development is a non-sense reason to give another delay.