Yes, higher orbits would have increased lifespan, a little bit longer for satellites under control and likely decades longer for satellites out of control.

I think the primary motivation for lower orbits would be compatibility with cellular telephones. While they have gotten it to work at current altitudes, it must be a lot easier at lower ones.

Other reasons could be decreased latency, less overlap/interference between coverage areas, reduced chance of Kessler syndrome, decreased power usage for transmission & reception.

Having them as low as possible improves latency, which is a big selling point of Starlink over incumbent geostationary services like Hughesnet.