As you said, these require a lot more on the marketing/partnerships side, rather than the technical side (in fact, one of the great things is that MVPs can be built in a couple of days on something like Wordpress).
Nailed it! What others have you noticed?
Now that I think about it, that actually describes a lot of blogs/vlogs/podcasts too (create an audience with great content, monetize via advertising). Not quite SaaS, though, so slightly different from OPs original question.
Places like https://designacademy.io/ sit in the middle - content-first to create the audience, then use that audience to sell online courses in your given niche.
The takeaway - which applies to any business really - is that you need an audience and you need to be selling something that someone desperately needs (rather than something that someone "wants").
Recruiters need candidates. Advertisers need eyeballs. Companies need investor networks. Find the need, build the audience.