Andrew Ng is one of Coursera's founders. He's big on learning as the development of habits...in American educational philosophy this idea can be traced back at least to John Dewey with academic formality. So it's not surprising that Coursera often chooses fixed schedules and cohesive cohorts over self-pacing. Indeed, Ng's most popular course,
Machine Learning is open enrollment, but not self paced and sends reminders when the student falls behind schedule.
That said, there are plenty of courses on Coursera where the materials stay up and online for years. But there's nothing wrong with teachers controlling how, when and where their course materials are accessible, and since many of the courses are from private institutions, e.g. notably Ng's Stanford, tax paying and citizenship (two orthogonal concepts orthogonal to accessibility of course materials) are mostly tangential to major MOOC mechanics.
It's absolutely amazing that the resources are so freely available and high quality. I am not sure where one would get standing to make demands upon the private entities providing them.