They’ve got the maintenance issue with the jets too, these jets need a massive team to keep them in use. They require so much resource which isn’t feasible for the Ukrainian army. Also, the major issue with these jets is for them to “work” they will need to enter Russian aerospace. It’s one thing having NATO supplied equipment in Ukraine but as soon as the NATO equipment steps foot in Russia/Russian aerospace, NATO is officially a party to the war and I don’t think this is a move NATO and the west want to take right now.The reason why USA jets may not be sent is the same reason for ours ; they are the most high-tech in the World, and pilots in Ukraine won't know the flying controls & also if one is shot down then the Russians will be able to study the technology?
Having said this, I reckon Zelenskyy will get his wish eventually, but not right now.