"Demilitarization and denazification" was the justification for the war, and is really the only way their full war, which has been costly in many ways, makes sense. Pre-war negotiations with NATO included demands far wider than just Ukraine. There's a chance things are being misinterpreted in terms of wording, but it sounds like demilitarization has been softened and any agreement would involve accepting the existing Ukraine government ("nazis"). There are also nuances about recognition of DPR/LPR, Russia's preferred version previously would have essentially given veto power over Ukraine government decisions. Losing that means they need a different form of leverage, such as replacing the government ("denazification"), with constitutional guarantees being a far weaker option.