I believe if life is common than there must of been at least one group of aliens that at least attempted to colonize it self everywhere in space?
Unless humans are a extreme anomaly and that most other aliens don’t really care about space exploration, and just focus on their home planet.
The thing about Alien structures in space is that they're not obvious, for all we know Tabby's Star could be a Dyson swarm
https://en.wikipedia.org/wiki/List_of_stars_that_dim_oddly
It also starts with the bizarre assumption that the structures would radiate heat that we could detect, which if you're a hyper-advanced species capable of building mega-structures seems kinda like an oversight and a waste