Maybe it's because I've only raced in areas that are within a few hours drive of Boston, but the Disney policy on others being able to pick up bibs was the exception, not the norm. Even our local Color Run was saying only racers could get their own bibs, nobody else on their behalf. So I'm used to policies like this.
And I agree, it probably boils down to three things... Runner safety, event security, and insurance. People who race under other's bibs have the incorrect safety information attached to their bib. If they're injured or incapacitated, Disney doesn't begin to know who to notify. And tied to that, if anybody can pick up bibs with easily forged/duplicated information, the overall safety to other runners is diminished. That impacts event security, and makes it easier to camouflage the identity of people who'd be intent on causing issues.
And, you know, it could be the event's insurance provider that may require it. We had local races here, just little ones, and their insurance providers all suggested or required this change.
So... I don't know. I'm OK with this change. And I think it'll really cut down on those unauthorized bib transfers.
As far as the bib transfer issue... I'm also OK with not allowing that. These are already high-demand races. By giving people a way to buy them and resell them, these races will sell out much, much faster. I think that stopgap is needed. For those who are unable to race, they do have the deferment process, which I wish people relied on more.