Why are all of them blinking on and off exactly the same?
They’re a bunch of individual moving points in a 20 second time exposure, so they look like lines.
That's a very good question! Using today's digital cameras it's often not possible to take long time exposures (keeping the shutter open for long periods of time (minutes) like in the old days using film cameras). Nowadays when taking sky photos with digital cameras it's common to take multiple exposures many seconds long and then stacking them all together to make a single photo. Wish I had a way to post photos I could post some I've taken this way of the Hubble Space Telescope and other satellites.
Anyway, satellites don't don't blink regularly like this unless they're tumbling, and operational Starlink satellites don't tumble.