For so many reasons.
I'm not saying they should go from specializing in one even to four or five, but at least compete in two closely related events. First, it would probably make training as well as competing even more enjoyable for them. It would take some pressure off because they wouldn't place all of their life's worth on that one result from that one race. It would simply give them more variety.
I've been having this thought lately especially regarding 400 hurdles/400 runners. Michael Norman and Rai Benjamin train together regularly, so there is obviously easy enough access to a coach, but why not have Mike try the hurdles? I understand there's technique involved, but as long as he has decent flexibility, he's an elite athlete and should be able to pick it up given enough time. If Norman has at least 0.5-1.0 seconds over Warholm in the open 400, I feel like he has solid potential in the hurdles...
This is even MORE true with the women. Shaunae Miller-Uibo, when she's in sub 49 shape, should be able to break the 400h world record immediately. I think the criticism of the women's 400h height of 30 inches is fair, and Miller-Uibo is literally 6'1", she could just step over them. Work on her stride pattern for a few weeks and it's done.
Everyone is seeing what Kerley is capable jumping down to the 100 and 200. I actually really appreciate his attitude and his self belief in wanting to be at the top in as many events as possible. When everyone was praising Boling and Carl Lewis as the only sub 10/8m+ long jumpers, Kerley said he wants to go jump 8m. Why don't more athletes have this attitude?
If Kerley is running 9.7s and getting beat in the 200 by Lyles and Knighton running 19.4-19.6s, what does that tell you about Lyles and Knighton's 400 potential...Unfortunately, short sprinters never want to make that move...
I've never believed in this 'pigeonholing runners into 1 event' crap. But ultimately it's up to the athletes wanting to branch out.