Why are the symptoms of the coronavirus markedly different when compared to other flu and cold-like virus-caused diseases? Why are most coughs in the more common cold and flu-type diseases characterized as phlegm or wet cough whereas the cough associated with the coronavirus is characterized as a dry cough?

This is in the nature of the pathology induced by the virus variants in question. The coronavirus is more insidious. It causes direct functional changes in tissues with relatively less triggering of immune responses, so what is associated symptom-wise with pulmonary infections usually involves a significant inflammatory response and an immune system counterattack to produce it. That is what triggers mucus production resulting in a wet productive cough, as opposed to the dry cough which is direct tissue irritation by the virus but in a more insidious way. The end result is that there is greater penetration of the cells of the body with more local damage resulting, because the immune system is less effective to resist the onslaught. There is nothing suspicious in this. These are, in effect, separate diseases and should not even be compared to one another.