I would say it's because of who you are. I don't think you would be much different even if you were younger than them.

It would be nice if we could just at least hand them one of our many lives, wouldn't it? We have so many we wouldn't notice it, but for them it would make a great difference without trapping them in this kind of live.

[Ikki says nothing to Marco's comment about how tired he feels, he's not surprised by it. Marco is older than him and Ikki's sure he has gone through the cycle more times than Ikki has already. If he himself feels tired of existing already at times, what won't Marco feel right now? Unfortunately, that's a tiredness that is bond to be with them forever, even if they weren't here... There's no rest of existing for a phoenix.]

Everyone is bond to lose someone sooner or later, that much they can understand. But most of them still have the comfort of knowing that they will join with their loved ones one day when they die. I guess Ace didn't stop to think about that part.

[About how, if there happens to be an afterlife in their world, Marco will probably be the only Whitebeard pirate to never join there.]