Russia's reasons for leaving the grain deal is that Western countries have not moved to lift the sanctions off of Russian grain and fertilizer exports as was initially agreed to when the deal was first struck. Russia has seen no promising signs that these promises would be fulfilled but remains open to reviving the deal if the export issue is resolved.
Despite Russia's claims, Western countries have provided Russia with a comprehensive guide of how a series of exemptions had been issued on the country's grain and fertilizer exports. Russia is using the stoppage of the deal to seek more concessions.
There's a 5% chance that there will be a bilateral cease-fire or peace agreement in the Russo-Ukraine conflict before 2024, according to the Metaculus prediction community.