I think cartridges like the 7mm-08 and .270 WSM have stolen much of the 7x57's appeal in the sporting arena.
THis ^^^probably deserves repeating.
We shooting types have been flirting with 7mm rifle rounds, from around 45mm to 60mm long cases. The wide array of rounds just labeled "280" being a good example, along with all the "6.8" labeled loads. And, of course, none of "us" can quite agree on whether it ought be a 'milder' military round, say 7x45; or an anti-game lightning bolt round closer to 7x60. So, what have "we" done? Well we've brought out every variant between those envelope edges. So, we get contrasts like .276Ross and the 280nato, and the 280rem, even the 276pedersen.
The 7x57 is kind of a middle-of-the-road answer.
Which has onuses like being "old school" or "not made here" to bias against the thing. It did not help that it was introduced at a time when militaries were torn between 6.5 loadings and "full power" cal..30 loads, so the 7x57 started as a bit of an orphan as was. The world then embraced all manner of "intermediate" cartridges, with varying amounts of public acceptance (or insistence).
And, of course, we ought not criticize, nor ostracize, any round a person adheres to successfully. Now, how the ammo companies sort out the economics of cranking out only a few thousand of each of the various kinds of thing we shoot, whether as assembled ammo or components is a different thing.
Perhaps, all that 7x57 'needs' is a self-loading platform, say something based on the AR-18--like as not, the hardest part would be engineering the magazine (something that gets skimped upon all too often).