I don't know that its scope manufactures aren't trying hard enough, any more the industry demands so much crap on a scope its no wonder basic FFP scopes weigh 24oz+.
By the time you put a 30+mm tube on the scope, giant objective lens, great big dial turrets large enough to have clear markings, locking and return to zero mechanisms, zoom throw lever, battery for illumination, circuitry for illumination and the illumination mechanism itself, enough shock control for the absurd abuse tests people do any more, and a big parallax adjustment dial on the side there just isn't any room for a truly light weight scope anymore. Or at least the industry at large has no incentive to really work towards one.
Not being designed to be directly and intentionally abused doesn't equate to fragile in my mind. Too much focus any more on stupid tests. Tests like can I zero this scope, take it off, use it as a hammer to build a house, throw it down the driveway, drive over it with a semi, remount it and still hit steel at 400 yds? No? Well this $300 scope is trash. I get the worry people let creep in that if they drop their rifle on that once in a lifetime hunt, they wont trust the shot when it comes time, but there is a difference between a scope that survives dropping your rifle\slipping and falling on it and needing to have a scope that can survive tossing your rifle off a cliff.
I still believe the scope industry peaked with the VHS-4323-LR (with regards to sub $1000). FFP, non illuminated, 32mm objective, 2.5-10 zoom, capped turrets, excellent glass, and numbered standardized (in this case MOA) reticle, under 17oz. The only thing they could have done better in my opinion was put shorter turrets on it so they didn't stick out so far. But given the current industry and what people buy (and probably never use half the features of) its easy to see why this option disappeared and was sold at heavy discounts after only a year. Granted I haven't subjected these scopes to the absurd torture listed above, but none of the examples I own have ever needed to be re-zeroed once setup unless they were moved to another rifle.
As for light rifles sucking past 300yds, hmmm, cant say I have the same trouble with any of my ultralight setups. Sure I'd love to have my heavy barreled rifles on those longs shots, but I am not dragging those heavy tack drivers around for 80 miles worth of hiking in a single week. The difference in accuracy isn't large enough to warrant that.