Why don’t digital TV streams fill all of their ad slots?

Despite all the hype around the digital streaming of TV content, networks still leave many of their digital ad slots unfilled. Given that leaving users to gawk at a network logo rather than being monetized through a served ad is a lost revenue opportunity and off-putting user experience, it is peculiar that this practice still occurs. But sources say that brand-safety concerns, small digital audiences, lack of measurement and complex legal issues have given networks little incentive to fill the remainder of their digital ad slots.