Lack of promotions, is often used as an excuse for songs not reaching some expected target.
But that's a weak excuse.
Promotions are as much a choice and part of a comeback, as the songs, the costumes, the MV themes etc. are.
The agencies/groups choose the promotional strategy.
At least the groups on the lower tier may not have resources and options, but BTS, Twice, Blackpink, IU, BigBang, Jhope kind of names, they explicitly choose how and how much they will promote or not.
Like they choose the song, the lyrics, the choreo, the costumes etc.
So blaming lack of promotions is no different from blaming bad choice of the song, boring choreo etc.
It is as much a judgment call, as other things that make a song release.
If the agency chose not to promote then maybe they misjudged the popularity of their brand name or the quality of the song.
Either way, promotions are part of the package, and lack of promotions a poor excuse for the underperformance of the song