With the easy access to camera and video via mobile phones this is going to happen. People may well have been filming before he collapsed and just continued catching a piece of history. If the worst had happened this footage may have provided critical evidence.
I'm not sure this is a new phenomenon since cameras and film were invented we have seen war correspondents capturing harrowing images for perpetuity.
If it is recognised media is it viewed differently to a member of e public filming it?
I agree with you re bystanders not helping, but this can sometimes be about that person being unsure what to do, particularly in an organised situation where medical staff and officials are on hand. I made the comment to my wife that people were filming it when I first saw it, but on viewing the full story on the news I'm not sure that they were, it looked like they were trying to look for something on their phones, possibly an emergency service number
Hopefully the athlete will fully recover and compete again. Interestingly officials said at least one athlete in all marathons collapsed and is unable to finish.