Marketplaces classically suffer from the chicken and egg problem. No point in distributing via marketplace if no one is buying there, no point in trying to buy there if no one is distributing (this is true even if "buying" is free).

For open-source stuff, npm is pretty much the One True Way to distribute JS libraries these days. If I'm looking for a component, I'll expect to find it by google and install it from npm.

(As far as Structor itself, I'm not at all clear on what it's supposed to do for me. The article is very long and covers too much ground. I don't see myself as likely to use a UI builder in any case, though. My current React work is all with bespoke UI controls, look of which is given to me by a designer.)