General Motors is pulling its Maven mobility service from eight US cities, including Boston, Chicago, and New York, leaving it with just nine 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 its 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 rental 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…