One of the main draws about a device made by Google is the ability to unlock the bootloader to have the freedom to root and install custom kernels and ROMs.
That should be no difference with the Pixel 2, but it seems that some devices purchased directly from Google have locked-down bootloaders. While it may not necessarily matter to a majority of buyers, many like to load custom ROMs on their device to introduce new features and it may be disappointing to some people not being able to do this.
The original Pixel from last year saw a similar situation with a locked bootloader on the Verizon model. Typically these devices have locked bootloaders so it could be that Google may have unintentionally shipped Verizon SKUs to some customers instead of the Unlocked version. A thread has been opened on the issue tracker with users experiencing the problem.
It seems that only the smaller Pixel 2 is impacted with noone reporting the same behaviour on the larger Pixel 2 XL.
Google is yet to comment on the situation and if those who find themselves with a locked bootloader will be able to get a replacement device.