They probably didn't do it because of the shit LISK had to endure after doing this. Because there was not a signle address where the coins were sent it was difficult for the community to check whether the coins were really invested or not.
As a result they had to post screenshots and videos of the vault to prove it.
This method works fine and there is only a 15 minute windows where the coins are not in multisig as they have a script running to send the coins over.
Yes, this method seems pretty transparent. I can simply plug in the address that I used for the ICO into a block explorer and verify my funds were sent from the hot wallet to the multisig. If there was any skimming going on, I am sure that this would be brought to light rather quickly.