Well, I suspect they talked to their legal department which _might_ have reasoned like this (IANAL, btw):
"Opus is a hybrid codec that internally uses both, SILK and Celt.
SILK was created by Skype (now Microsoft) and its patent license includes this gem: '5.1 Skype may terminate this License Agreement and any rights granted hereunder in the event that you or any of your Affiliates (i) materially breaches any of the terms and conditions of this Agreement; or (ii) asserts any patent or patent rights against Skype, its Affiliates, or its or their successors or assigns.'
So lets assume Motorola (owned by Google) tries to (counter)sue MS over some Android stuff: Suddenly the patent grant given by Skype becomes invalid and Google might have to remove Opus from Chrome. If it's popular by that time, this is a serious competitive disadvantage.
So better not help making it popular in the first place. "
Skype/MS should just make it fully open source then, for the betterment of the web, instead of using it for potential silly legal fights in the future.
"Opus is a hybrid codec that internally uses both, SILK and Celt.
SILK was created by Skype (now Microsoft) and its patent license includes this gem: '5.1 Skype may terminate this License Agreement and any rights granted hereunder in the event that you or any of your Affiliates (i) materially breaches any of the terms and conditions of this Agreement; or (ii) asserts any patent or patent rights against Skype, its Affiliates, or its or their successors or assigns.'
So lets assume Motorola (owned by Google) tries to (counter)sue MS over some Android stuff: Suddenly the patent grant given by Skype becomes invalid and Google might have to remove Opus from Chrome. If it's popular by that time, this is a serious competitive disadvantage.
So better not help making it popular in the first place. "