Maybe companies has a agenda with not implementing multisig. That they not want to lose the control of the funds people use through their service. Its not good, but when companies starts up in unregulated business areas, they are not implementing tools that makes them to lose control. Unless a other does it and they have to follow to not lose market.
..... and made this an exchange not just some id to address type. With this multi-sig, you would be the first mover in this area, forcing companies like bit-pay and coinbase to take notice and hopefully implement it.