Because you don't need that kind of training to do this passage on your own. If you want to go, you go. Many do, some don't make it. Preparation+Luck, etc. If the rally organizers only purport to offer t-shirts, some weather routing and a party in the BVI's at the end, then the rest is up to the skipper.
I'm not a rally person myself, I'd rather pick my own weather windows and not have to worry about getting to a party by some time, but I do think that there is room for this level of event. Should folks be more prepared for what is a pretty serious offshore passage? No doubt. Is it the rally organizers' responsibility to make sure everyone is prepared? I don't really think so other than offering suggestions.
If the loss of boats in a given rally causes participants to realize that they are not actually much safer out there just because they are in a group, then that will probably mean fewer boats in the rally next year, with a greater emphasis on safety, which is a good thing. This will continue until the memory of the lost boats becomes shrouded in the mists of the distant past (typically ~ 5 years) and then once ill prepared sailors will start to fill the rally's numbers. Still, it's the skippers responsibility.
You can lead a horse to water and so forth.
You only have to do a single rally or race with hundreds of boats to understand how big the ocean is. For the first few hours, it's sails all over the horizon. The next morning, you might see couple. The next, probably none. The notion of "sailing in a group" is a very loose notion out there.
But I do think you guys have hit on an important issue. Though the rally organizer leaves the safety/seaworthiness responsibilities to the skipper (which is good) - they do, in fact, impose a schedule just like a race. And this inevitably means that the risks are higher. Yet, unlike a race, these risks are assigned across a fleet that is VERY uneven, and unverified, in terms of preparedness.
Where the race operates under ISAF regs, the rally doesn't. Is that good for sailing?
Sure, the argument is that such safety regs will reduce the number of sailors participating in a rally. Is that a bad thing? What are the motivations of the organizers of a rally vs. a race? Aren't there financial incentives for both? Yet the liabilities are different? How do corporates sponsors look on the issue of the organizers of one activity insisting on safety and another not..especially when things go wrong?
I just think there are some very questionable distinctions being drawn in the rally vs. race conversation.