Zoom meetings are more demanding cognitively than face-to-face meetings, which rely a lot on visual cues. It is easy to tell if people are paying attention, whether someone wants to speak, whether they are agreeing or disagreeing, and so forth.
In a Zoom meeting, it is much more challenging to read people: Are they following along, bored, engaged, in agreement? There is no eye contact or shared eye gaze to provide these cues. Even if people are explicitly nodding or raising hands, it takes extra effort to scan through all the people.
Some people have their cameras turned off, and sometimes there are more people than an array can fit, making things even more challenging. There is often a temporal delay. All of these factors make it necessary to consciously think about things that normally would be fairly automatic.
Another factor that people tend to be aware of is that there are many distractions that are not always present in face-to-face meetings—self-consciousness about one’s appearance or room, disruptive pets, and children. It’s also tempting to respond to emails or work on the laptop; if you’re muted, no one will notice. Sustaining attention is harder when trying to avoid distractions.
There are also other fatiguing characteristics of video conferencing that are less discussed in the media. In face-to-face meetings, there is usually some gap between a previous meeting and the next one, providing a natural cognitive and perhaps physical break. People cannot focus on difficult cognitive tasks for extended periods of time, and research suggests that they will be more alert and have greater capacity to think after a 15-minute break (especially one that involves physical activity or the outdoors). Zoom meetings that occur back to back are too taxing for your attentional system.
Finally, uncertainty and stress can lead to distracting thoughts and poor sleep quality. Both of these factors, in turn, make sustained attention taxing.