I started attending house concerts over 10 years ago. They were hosted by a friend I knew from the local music clubs (north Dallas area, at the time). The first performer I saw was an artist that I knew, but most of the performers were new to me. As it turns out, this just didn't matter.
For me, the lure of the club was always the music, but there is nothing more disappointing than struggling to hear the music over the club noise. Artists tend to get to a place where they are "just getting through the gig" in this situation. There's little point in trying to relate to an audience that doesn't realize the song has just ended. Artists, on the other hand, want to engage with the audience, to feel that their performance is the sole focus of the assembled group. House concerts provide that opportunity, and the artists' perception of this usually results in extraordinary performances.
In addition, a house concert venue effectively removes all constraints from the performers. If they want to try out a new tune (or even a new instrument) to gauge our reactions, we will be treated to new music before anyone else hears it.