I think the reason that most people focus on marketing instead of improving their work is that marketing promises a quick fix.
It’s shiny and fancy and promising with all the SEO, funnels and mailing lists.
Compared to that, the hours and hours of simply beating on your craft don’t look as attractive.
But that is exactly the point most people are missing (or actively avoiding): Mastery requires hard fucking work. There is no way around it. Period.