This boosts actually requires 3 man and some time to execute. So if you rush the bomb, its a no-go for the boost, as 2 boosters are exposed for enemies. Also, even if boost is done you can counter with 1 or 2 flashbangs at same time, or spam the pixel through the wood, or molotov from above... so many possibilities.
The reason why they didn't counter its because the boost is brand new, kudos for FURIA for discovering it. Now pro players should be aware to play around that "new" position and with time it will be just like the "out of the building" boost.