It all returns to diesel. Kiev is attacking Russian gas while Iran is restricting flow through the strait of Hormuz, leading supply to get lower and lower. The US wants to relax restrictions on Russian gas in order to alleviate the supply problem, and Kiev is insistent that their attacks on Russian gas have nothing to do with rising diesel prices and lowering supply and are blaming it solely on Iran and the strait of Hormuz closure, because they want to hurt Russia economically while maintaining legitimacy in the eyes of their allies that depend on diesel.
The vassal won't get in line, so the empire pulled material support as a disciplinary measure. Europe does not have something that can serve as a meaningful alternative to this, leaving Ukraine, as always, at the mercy of the US if they wish to continue fighting, rather than reaching a negotiated settlement as more and more countries are desiring (including Ukraine's working populace).
All of this from the US empire's hubris, thinking it could support both a war on Russia and Iran without consequence. No need for conspiracy theories about Trump and Musk being Russian agents, the truth is that they only care about keeping the empire going, which requires stableized fuel for the global economy. The US can either surrender to Iran, or wind down sanctions on Russia. Otherwise, the entire world economy stands to go to chaos.