Third is that some users will have enough knowledge of epoxy to know it discolours (badly) with UV exposure, so a clear epoxy fill will eventually look just plain awful. The related reason is that maybe some users know getting the fill completely bubble-free can be tricky* so they're afraid to try. The first is just because people don't want to make their fills transparent (or to put it another way, they really like coloured fills), at a guess this would account for most of it.
EPOXY WOOD SLAB CRACK REPAIR VIDEO PLUS
Two related reasons I can think of plus a third unrelated. Why is clear epoxy not used? What considerations should go into a decision about whether, and how, to tint? Since it is done so rarely I assume there must be a reason, and don't want to ruin my slab due to my inexperience, so: I've done some googling but in addition to not seeing any examples, I also cannot find any discussion of why tinting is so common. However, I have not been able to find a single example of clear epoxy being used.
I was considering using the epoxy without a tint so that the reinforcement is relatively invisible, and went with the 207 hardener for this purpose. It creates a very striking aesthetic effect, but I don't think I want to pull the visual focus away from the wood like that. The thing that has surprised me in the videos I've seen is that all of them use a very dark tint, many going with straight black.
I don't like the look of butterfly keys, and I don't believe that this crack needs much reinforcement, but I was going to fill it with West epoxy just in case (and as a way to finally try using it). I've worked with a few live edge slabs in the past, but the one I have now is the first one with a sizable crack.