However Skype had no history of running servers. Just keeping the login servers up and running (a handful of them) was enough of a challenge.
Plus when the company's success and revenue was driven by the P2P team and they said the same layer will work for messages... there was no one strong enough to argue.
And when it was obvious that Skype messaging was sub par, the company just went in denial. "We aren't really competing with Whatsapp, because they don't do video" got us another year or two of not doing too much about the root cause.
It was after the Microsoft aquisition when some MS architects told the engineers upfront that p2p and realtime messaging - forget about it.