They are young stars who are being built up as such. This isn't anything new or surprising. This is how TV works. This is how TV has worked with the NBA since Bird and Magic came on the scene. The Celtics hype for this year was built around Hayward and Irving. Hayward was gone after the first game, and Irving's injury left 0 established story lines for national Celtics coverage.
I've got a news flash for you: LeBron gets constant tongue action from the national media, too. So, if it's Boston v. Cleveland in the conference finals, you can expect to be upset by that coverage, as well.
You want more balance, and you were looking for the local Celtics coverage?