Sure, as a total fluke in a very specific industry, software might sell itself. Everywhere else, and especially in physical product and deep tech, someone has to fully own the sales side of the business including the really time intensive stuff like website, email marketing, conferences, merch, sales meetings and trade shows. Heck, even viable solo founder companies would probably sell a magnitude harder with a sales co-founder.
Anecdotally my company picked up a few big distributor contracts for software tools and deep tech products, stuff people want. The products are done, high quality, but they don’t sell themselves - we have to actively put effort into outreach for every sale. Think about that in the context of your own startup. Building the thing is not the end hurdle, it’s kind of like a dependency to selling the thing, which creates revenue.