In Chapter 1041 Momonosuke reveals to Yamato that Oden tore out pages with crucial information from his logbook for an unknown reason. Because of this, Momonosuke is afraid to open up Wano to the rest of the world due to the potential danger it may face.
One possibility is that Oden tore the crucial pages from his journal and entrusted it to Toki so that she could understand the whole picture why she needed to send Kinemon’s gang into the future. So the papers handed by Oden in Chapter 972 were the torn pages already plus his letter to Toki. Then after reading the pages, with Oden’ message, Toki destroyed the papers completely so that to protect the information from the enemy.
Another possibility is that Toki tore the pages. In this case Toki is the one who left Oden’s journal for Yamato to find. Why would she do either thing?
Toki was already on a mission to go to Wano for some great purpose that caused her to leap forward hundreds of years. After meeting Oden, she no longer seems to have that mission. The main pupose that stands out is that she didn’t want Oden to return or stay in Wano when Orochi and Kaido came to power.
Toki realized something about her mission that made it imperative for the situation in Wano to become what it is. She had been manipulating things subtly, not for nefarious purposes, but for the greater good, even when that comes at great personal expense. She therefore took out those final pages as a means to further guide someone, Yamato, to travel and see what Roger and Oden saw.
So all of this reinforces the belief that Yamato will be the next member of the Straw Hat Pirates crew. It’s already been established that Yamato’s dream is to go out on the sea and have freedom and adventures. She has never been portrayed as wrong or foolish for wanting this (unlike her obsession with becoming Oden), and it’s pretty clear this is what Oda wants us to be emotionally invested in. We want Yamato to succeed in winning freedom from her father and going out to sea. Having her just stay behind in Wano would essentially rob the emotional catharsis of that event.