I'm 35, I'm far from a boomer... I just spent years working in music and know how things work - how you get that review, how you get that radio play.
Yes, word of mouth is a thing - but you still need to get that initial audience somehow, and just sticking your music on Spotify won't do it.
It's the same as any other business. I could set up an online shop selling t-shirts, but unless I put money into marketing who's going to find it?