Yea it is, as in this quote " it’s the only show in all of television, going back at least a decade, to post week-to-week ratings gains in key demographics for every single episode over the entire season."
But yes BBC America and BBC tend to have their heads up their rears regarding how to market and distribute their shows with modern convenience.
Amazon does have it for per episode prices.
Hulu is going to have it later in the year(no exact date, late 2018), not sure why wait so long.
Basically this show is heavily torrented and streamed elsewhere(guilty), they need to get their act together as it came out back in April. Movies are available faster then that.