Most developers I know don’t care about business. At all. They have zero business knowledge, not even common sense about what business is all about.
Some of them that work in big companies think that marketing is evil.
Some people even call marketing emails “spam”, even though they signed up voluntarily to receive those marketing emails.
By the way, let me define spam - it’s unwanted emails from Nigerian princes that need help getting their money from a bank. Or enlarge-your-whatever kind of emails. Or emails from girls you don’t know. Or unsolicited, mass-sent promotional emails to which you didn’t sign up for, that don’t have any “unsubscribe” link. That’s spam.
Anyway, I think that marketing is a very useful skill to have as a developer.
Why? Because you have a special position and very powerful combination of skills if you do so.
Most developers will stay in that “marketing is evil” kind of thinking, and never try to get out of their comfort zone made of editor config files and best practices.
And that’s fine if all you want is to work at a company managed by someone else, and do your work at the keyboard, forever and ever.
But what if you have an idea, and you want to bring it to market yourself? On your own?
In this case let me say that if you are a mediocre developer and you are mediocre at marketing, it’s way better than being a stellar developer and have zero marketing knowledge or interest.
And imagine what you can do if you are pretty good developer and you can become pretty good at marketing.
That’s a very, very powerful combination of skills.