The deal that the creators of “The Expanse” cut with Syfy was focused on live (aka: “linear viewing”) on Syfy with streaming happening on Amazon Prime.

I am not expert on the specifics of how TV production and airing deals are cut, but the first article you link to states the following; bold emphasis is mine:

“The cancellation decision by Syfy is said to be linked to the nature of its agreement for the series, which only gives the cable network first-run linear rights in the U.S. That puts an extraordinary amount of emphasis on live, linear viewing, which is inherently challenging for sci-fi/genre series that tend to draw the lion’s share of their audiences from digital/streaming.”

This other article on the cancellation on Quartz explains it well; again, bold emphasis is mine:

“The series seemingly got the axe because of a complicated rights deal that put an inordinate amount of pressure on the show’s live-TV ratings to make it worth it for Syfy.”

And this:

“The show airs first on Syfy in the US; viewers can watch live on the cable TV channel or through its app with most pay-TV subscriptions. Past seasons are streamed on Amazon Prime in the US.”

So it seems like the pressure to get people to watch the show exactly at a specific time on a specific day — which is very archaic for today’s streaming age — made it a losing prospect for Syfy. In contrast, Amazon Prime is more of the modern TV model; which is all based on streaming.

In the end it seems like streaming won. And it doesn’t seem that the deal with Syfy accounted for streaming or the offer of streaming rights was ever extended to them.