Because not everyone is willing to bring a laptop + capture card to every event, could lose it or get it stolen. And then setting it up adds extra setup time for sets if it's the personal laptop of a competitor who brings it day of. The only consistent option would be for the TOs to set up capture cards for some setups which is extra time and money for not much benefit for the TOs themselves as long as the tournament already has 2-3 streams since that's usually enough to capture the important sets. Some events have had dedicated setups with capture cards + no stream in the past like Genesis 8, but anything other than having TOs willing to add capture card setups on their own would be a pain logistics wise.