Weren't those restrictions placed because of concern they would escalate the response from Russia- remember Russia threats to use nukes? Was it not only when China, Russias new owners, clearly told Putin he cannot to use nukes that Ukraine has then been able to bomb/and more recently actually take Russian territory? https://www.telegraph.co.uk/world-news/2023/07/05/xi-jinping-warns-putin-nuclear-weapons-china-russia-ukraine/ This is a proxy war between China and the US but both super powers are not keen on it becoming a direct confrontation which would then have serious trade consequences for both sides.