This is not the Jetsons. If Ukraine had a robo-army, by now there would be no "busification". And yes, Russia is losing more men, but why do you think that is? It is because the Russians are attacking, breaking cover. If the Ukrainians attacked, the same would happen to them.
It may be that the Ukrainians have superiority in autonomous targeting drones; that the Andurils and tech startups of the West help them in this. But how long do you think this superiority will last? Will this period be long enough to enable the Ukrainians to break out and get the the Donbas back? What do you think will happen to the casualty exchange rate when Ukraine attacks?
Yes, drones can help attack, but they cannot hold land. That requires men. Again, we are not in the Jetsons era yet.
Look, Ukraine is already in a demographic death spiral. Using EU funds, it is importing guest workers, already reluctant to enter a warzone, while shipping of it's own youth to die at the front. Ukraine is desperate to involve the West more deeply in the war. This is unsustainable and dangerous for both itself and the West.
Say, your plucky smaller friend is getting trashed in a bar fight with a big guy. He is gesturing at you frantically to join in. Won't the wise option -- for him and for you -- be to urge him to stop the fighting and try to come to terms with his opponent? Rather, the West keeps slipping Zelensky the equivalent of knuckle dusters, tells him "Keep going", "punch him over there", "look out for his left hook", and swears at the Russians while quietly buying uranium and gas from them. Rocky Balboa's coach is doing business with Ivan Draga.
Those Ukrainian defensive lines you speak of, the ones that are too sacrosanct, they are no guarantee. The Ukrainians need to scramble and build new ones behind them anyway. The Russians are still advancing, imposing losses on Ukraine's assault brigades that have taken back territory in the last two months. The Ukrainians aren't going to get a dramatic infusion of soldiers. So they need new lines far in the back anyway, either as defenses after surrendering territory, or as fallbacks if the frontline is breached. The West should help Ukraine build new lines in the back (the only real security guarantee), encourage them to make concessions for peace and broach the topic with the Russians