General Motors is pulling its Maven mobility service from 8 US cities, including Boston, Chicago, and New York, leaving it with just 9 active regions. It’s not a good look for Maven, which was meant to be a trailblazer in showing the world the value of new mobility-focused services. GM’s Cruise seems to be living up to the hype, but the vehicle-rental offering at the heart of Maven seems to have missed out in a big way. Maven has a number of rivals. Daimler took a similar angle, with its car2go subsidiary, but Getaround and Zipcar are independent of an automaker. There’s no shortage of such services, but when a company as influential as GM can’t make it work, things…