Well, to be fair its been less than a week since the news was dropped. And on a Sunday morning no less. based on the Twitter reactions a lot of people are still finding out and many viewers still might not know.
If someone starts a petition, I am sure us related fan sites and maybe even some cast members might signal boost! But for some reasons I already outlined plus others, Ripper Street is a tough comparison. That show had two full series' run, with a fan base on both sides of the pond who had a strong network to mobilize. The Smoke hasn't been picked up anywhere else yet so its online presence is smaller. Plus, if you read the details of the Amazon deal, that Tiger Aspect (who produce Ripper Street) were in discussion with them came out a week after the cancellation news landed. I would be very surprised if that doesn't mean that they were already trying to find someone to pick up the show before they were officially cancelled.