The Snapdragon 820 versions of the Galaxy S7 and S7 edge ship with locked bootloaders, which makes rooting and modding near-impossible, while the Exynos variation already got root and recovery installed. Given that the LG G5 ships with the same processor in the US, it was largely expected that its locked bootloader will conform to the same strict tinker-prevention measures.
Well, maybe not. T-Mobile is renowned for trying to make their phones as user-friendly as possible, and has promised to work with Samsung on the bootloader issue, but it doesn't need to do so with the G5.
Enterprising developers are reporting that the T-Mobile version of LG's newest puppy is pretty unlockable, and the procedure is no more complicated than the one on a Nexus phone. There are still issues beyond the bootloader unlock, though, so don't get your hopes too high just yet, but the start is promising.