This is because the device does not have
a dedicated recovery partition, and thus the boot partition must be modified in order to install TWRP.
The device's kernel source code was released a little over 10 days ago which has allowed developers to build TWRP, but without official factory images, lack of
a dedicated recovery partition, and unfamiliarity with building TWRP for A / B partition devices, few dared to mess with their device in case it wouldn't boot anymore.
Surface comes with a built - in Windows recovery information, stored in
a dedicated recovery partition, which you can copy to or move to a USB recovery drive.
It is stored on
a dedicated recovery partition on your PC.