I wouldn't be in a hurry to blame mine on the fact that the drive is Seagate, as it's been plugged into the back of my iMac since 2012 without any issues of any kind. The only difference now is that the Mac recently changed from an early 2008 20" iMac 2.66 GHz Core 2 Duo to a 2017 27" 3.4 GHz Intel Core i5.
And that is when I started to notice the mysterious ejections with my long-time Seagate—a change to a newer iMac. I think there is some subtle (?) change in the USB voodoo and for some reason Seagate gets weird on occasion. As joemikeb notes, Seagate drives are different in their power requirements.
