The Second Age and the Third Age are 3000 years apart. The significant time gap means that the show will focus on a completely different cast of characters. While people of Middle-earth are unusually long-lived, such as Gandalf who lived for 2000 years, it’s not likely the series will feature many - if any - familiar faces.
Setting the show in a completely different era will allow the series to showcase a much different side of Middle-earth than what fans have seen before. Fans of the books and the films, and even former members of the cast and crew, have expressed dissatisfaction with the idea of revisiting the books and existing characters whose stories have already been told, so exploring the Second Age and introducing new characters could be the best direction for the show to take.