Work in AI-based explanation systems has uncovered an interesting contradiction: people prefer and learn best from 'why' explanations but expert esports commentators primarily answer 'what' questions when explaining complex behavior in real-time strategy games. Three possible explanations for this contradiction are: 1.) broadcast audiences are well-informed and do not need 'why' explanations; 2.) consuming 'why' explanations in real-time is too cognitively demanding for audiences; or 3.) producing live 'why' explanations is too difficult for commentators. We answer this open question by investigating the effects of explanation types and presentation modalities on audience recall and cognitive load in the context of an esports broadcast. We recruit 131 Dota 2 players and split them into three groups: the first group views a Dota 2 broadcast, the second group has the addition of an interactive map that provides 'what' explanations, and the final group receives the interactive map with detailed 'why' explanations. We find that participants who receive short interactive text prompts that provide 'what' explanations outperform the other two groups on a multiple-choice recall task. We also find that participants who receive detailed 'why' explanations submit the highest reports of cognitive load. Our evidence supports the conclusion that informed audiences benefit from explanations but do not have the cognitive resources to process 'why' answers in real-time. It also supports the conclusion that stacked explanation interventions across different modalities, like audio, interactivity, and text, can aid real-time comprehension when attention resources are limited. Together, our results indicate that interactive multimedia interfaces can be leveraged to quickly guide attention and provide low-cost explanations to improve intelligibility when time is too scarce for cognitively demanding 'why' explanations
