Emphasis on _some_. This type of behaviour is more common on the compact 2.5" type external drives.
As of writing this comment, big external drives still come with 3.5" hard drives, with the only caveat being that some require you to disable the 3.3V rail on your SATA connector, either by cutting the wire or taping some pins on your HDD with kapton tape. Without the workaround some of these shucked drives will not power up properly when connected to a SATA power plug that also provides 3.3V.
As of writing this comment, big external drives still come with 3.5" hard drives, with the only caveat being that some require you to disable the 3.3V rail on your SATA connector, either by cutting the wire or taping some pins on your HDD with kapton tape. Without the workaround some of these shucked drives will not power up properly when connected to a SATA power plug that also provides 3.3V.