Startup founder here.

I can expand on this problem in a bit more detail, but it comes down to one key term: cost of acquisition.

There are only so many ways that a website can improve traffic flow. The best is if the site somehow goes viral since this is nominally free. This is a longshot and not likely to happen.

There are places where you can share your site/app with a receptive audience. FB Groups, Reddit, IndieHackers, ProductHunt, and even Hacker News comes to mind. Whether it works or not is somewhat dependent on the audience of the property. For example, travel apps aren't particularly popular with the HN crowd, but my app was on the top of r/InternetIsBeautiful for a full 24 hours and my initial batch of users came from r/TravelHacks. These are good for "bursts", but hard to sustain because you can't just keep posting to r/TravelHacks or HN with the same link.

Then there are paid ads on various ad networks or through content creators. These can be quite expensive and often, the cost of acquisition for a single converting user can be quite high! In the early days, this may not be feasible, especially as you're still trying to figure out your audience. One of the startups I worked at had a CAC over $100 via Facebook ads (!!!), but the product was such that they would make it back in 3 months of a user subscribing; the basic math worked as long as they could retain the user.

Then there's SEO. Effectively, this is "free" as long as you can do it well since you'll naturally show up in the resultset for given search terms. Because so much of our user interaction with the web has been initiated from search, this is one of the few things that can be done to improve traffic and visibility. (I think this is changing with generations and with ChatGPT; younger generations may initiate their web journey through a social channel rather than through search.)

TL;DR: SEO isn't a "silly strategy"; it can be one of the most cost effective ways to get visibility because the cost of acquisition is cheap and works well over a long time scale compared to other options.