Turns out that Russia offered to withdraw to its pre-invasion position in exchange for Ukraine promising to remain neutral and not join NATO (Foreign Affairs).
Then Boris Johnson turned up in Kiev “almost without warning” to tell Zelensky “that even if Ukraine is ready to sign some agreements on guarantees with Putin, they [the West] are not” (Ukrainska Pravda).
Zelensky does not control his country. If he wanted peace, he would be accused of treason, removed from power, and replaced, by the West, with someone willing to keep throwing Ukrainian soldiers at the Russian army.