In the musician world, "build it and they will come" would refer to creating a really great band by practicing in your parents basement, but never playing shows in the real world. You aren't going to grow a fanbase by playing in the basement. But you could be a damn fucking good band playing music that everyone needs to hear. There is a lot of work that takes you out of the basement. 50%. But if the first 50% isn't there no amount of leaving the basement is going land you anywhere.
Musician equivalent might be identifying few notable bands in a given genre and actually understanding which fans spend money, why, where they listen to it, what other music they listen to, how they discover new music, what songs they share with people, etc; never done music R&D, so honestly stretch, in part because I know distribution is way more important than the actual music, but that doesn’t change that ultimately it’s the fans listening to music that matter. The “build it and they will come” would be making full album with music videos before ever letting single fan or peer familiar with fan tastes listen to the music.