There are definitely a few considerations regarding having video:

1. Security/confidentiality issues

Given the pervasiveness of smartphones, this can absolutely be a serious problem, but for most conferences, this is probably not the main reason to avoid video.

2. Speaker comfort, as @Jeffro mentioned

Although you can't argue with how someone feels, not having video is actually a false sense of security for those who care given the pervasiveness of smartphones. If it's the condition of a certain speaker(s) you really want, they can have their illusion. Just don't officially film their sessions, but you can still film others'.

That said, most speakers - paid or volunteer - will usually appreciate the extra exposure they and their one-off talk will get by living on in video online, and some speakers may even use it to check their performance with an eye to improving next time.

3. Attendance impact

Some people will choose to wait for the video instead of paying & coming to the event, no question.

But not everyone who wants video is a cheapskate. Some legitimately can't afford to come (yet!), some have prior engagements, some would prefer to take notes after the fact and some would like to show others what they missed.

4. Cost

Depending on the formality of the conference and its reputation, having a pro video crew can be a significant budget eater, especially if you can't get sponsorship for it. But again given the pervasiveness of smartphones, there's not much excuse for not having someone's high-end phone/tablet dedicated to recording each speaker, or even crowdsourcing the filming by asking attendees to upload their recordings for the organizers to pick and choose from later (giving credit where wanted, of course). If anything, the latter is an excuse to get & reward some community participation.

As for me, I'd never heard of PressNomics until I saw this post, so there's no way I could have paid for it even if I wanted to. But video would have helped me decide if I should go next time.