Performance work is mostly a measurement problem.

Not dishonestly. Measured in a way that happens to flatter, because the easy measurement and the useful measurement diverge and nobody has a reason to take the harder one.

The easy one is an average frame rate on a fresh, cool, recent device over a short run. The useful one is a distribution taken on an old device that has been playing long enough to get hot. The first is a number you can put in a store listing. The second is what someone holding the phone will feel.

Once you take the second one seriously, the work changes. It stops being about making the fast path faster and becomes about finding the rare slow path: the garbage collection pause, the shader compiled on first use, the texture upload that blocks, the allocation that triggers reclaim on a device with no headroom. Those are the frames people notice, and they are invisible to an average.

Why low-end Android specifically

Because it is where the gap between the two measurements is widest, and because it is where most installs come from in most markets. A game that runs well on a four year old midrange handset runs well everywhere. The reverse is not true, and building the other way around is how a title ends up with good reviews in one country and one-star reviews in five others.