Starfield is a game about a humanity in the early stages of interstellar travel and colonization, a game without living alien civilizationals. A hard science fiction game with deep roots in realistic science (with the exception of the grav drive and the temples/powers/unity).
It would be utterly unrealistic and unimmersive to have all planets full of interesting landmarks, structures or the like. Sure it could host relics/remains of other civilisations or stuff like that, but that would change the game on a fundamental level and would break the story of the game.
I love that space and most planets are utterly boring in Starfield, because that is the truth about space, it is huge, boring and mostly dead.
But I can understand everyone who thinks that this makes Starfield a boring game, there are lots of games out there that I think are boring (GTA 5 for example) which are loved by huge crowds of people.