If anything, making your own game engine makes process more frustrating, time consuming and leads to burnout quicker than ever, especially when your initial goal was just to make a game but instead you stuck figuring out your own render pipeline or inventing some other wheel. I have a headache just from thinking that at some point in engine development person would have to spend literal weeks figuring out export to Android with proper signage and all, when, again, all they wanted is to just make a game.
Speaking as someone who has made their own game engine for their indie game: it really depends on the game, and on the developer's personality and goals. I think you're probably right for the majority of cases, since the majority of games people want to make are reasonably well-served by general-purpose game engines.
But part of the thing that attracted me to the game I'm making is that it would be hard to make in a standard cookie-cutter way. The novelty of the systems involved is part of the appeal, both to me and (ideally) to my customers. If/when I get some of those (:
For any one specific thing, be it a doorknob, a rope, a sheet of paper or fabric, or a pair of scissors, there's probably a different design that's several orders of magnitude simpler and cheaper, and also much stronger and more reliable. Single-axis parallel grippers, circumferential chucks, vacuum cups/vacuum pads, electromagnets, cam lock and release mechanisms, and so on are common in industrial robotics.
Assume your robot's only task is to grab a spool with a 35 +/-0.5 mm ID core from from an infeed rack and place it on a spindle, you're not going to try to build a five-finger human sized servo-operated hand and tuck two of those fingers away to awkwardly pinch outwards from the inside, you're going to grab a Schunk JGZ concentric gripper off the shelf and plumb a pair of air lines to it. If it also needs to grab a tab from some tape on the spool and pull it into the machine, you're just going to add an asymmetric pincer like an angular tumor on two of the jaws - or graft on an entire separate parallel gripper like some polydactyl appendage, or tool-change, amputating and reattaching hands at will.
I have also observed that humans are quite good at anthropomorphizing robot arms: a small, well-tuned motion can be universally recognized as a nod of agreement, shrug of confusion, wave of acknowledgement, or sigh of disappointment, even if the equipment is a bright yellow 6-axis piece of cast iron with menacing claws where the hand (or face? they're often the same) should be. Googley eyes and a "Hi my name is" sticker make this even more convincing.
But if you need a single tool to grip a doorknob, a rope, a sheet of paper, a pair of scissors, AND an unknown variety of other arbitrary household objects... it's probably best to start with an approximation of the human hand. Also, while claws may be appropriate for a work environment with the robot inside a fence, in collaborative situations hands are just less intimidating.
Seems like a pretty high bang-for-the-buck for versatility and capability with only a few cables controlling it.
[1] https://arxiv.org/pdf/2303.09861