Is it possible that Volodymyr Zelenskyy sees war as a profit model for him?
Is he holding back because he wants the war?
For a long time, the US and other Western governments deliberately withheld from Ukraine any long-range weapons that could reach inside Russia, and for that matter a lot of basic offensive weapon systems like tanks. We basically gave Ukraine only enough support not to lose.
Even now, the single biggest disparity on the front is Russian air power, and it is very difficult to conduct consistent offensive ground operations when the other side has the advantage in the air. And we still haven't begun to provide the Ukrainians with even older-generation F-16's, so that disadvantage is going to be in place for a while.
They do have more drones now, but the reality is that drone strikes against civilian infrastructure are no more likely to get Russia to end the war than they were able to get Ukraine to surrender. The best use of those weapons if you actually intend to win the war is to use them against select, high-value military targets.
The problem is that such targets don't always make themselves readily available for such strikes. Also, because those munitions aren't unlmited, it makes sense to hold them until their military impact can be maximized. Most likely, that means striking at key communications and supply centers in Zaporizhzhia, Kherson, and Crimea only after the land bridge from Russia has been severed.
In other words...no. Zelensky isn't trying trying to prolong the war. This is just what a real war looks like.