“This was the case with Unity for a long time, but in the last few years the quality of that back half of development has rapidly declined, to the point where people are absolutely sick of their own projects by the time they’re finished… or more accurately, abandoned, because long-term maintenance of Unity games is appallingly hard.”
Unity is great for the prototype and miserable for the last year of the game. This comes from the guy studios hire to port and maintain games a decade later. Engines that hide their source turn every late bug into a support ticket. Unity sells the honeymoon and leaves the marriage to you.