It's a dog-whistle because it's a divisive trope and founded on many untruths. It seeks to scapegoat the older generation to the younger in much the same way as the opposite "youth are snowflakes with mental health problems" trope.
It's a dog whistle because its a massive generalisation that doesn't reflect the lived experience of many people.
Let's look just at education - the trope is that the older generation all got free university and the younger generation get stiffed by huge loans (this latter part is true and scandalous). Yet only 5% went to university and many left school at 16, even 15 and straight out to productive work. Now almost everyone stays in school for 2 more years and 50% in university for another 4 years. That's 6 years economic inactivity for themselves and the country. Hardly surprising that living standards fall.
Certainly younger people struggle with massive rents (as do older) but house prices are a function of low interest rates, suppressed during the financial crisis and also of the enlarged labour force. But thats hardly the fault of the older generation.
Yes, pensions have risen but that's a function of the stagnation and inflation within the economy not a policy of the aged.
You might say that the older generation have voted to dismantle the settlement (though what that means is nebulous) but generally the voters of any generation have little impact on the policies enacted. Politicians are considerably younger than the boomers you dislike yet seem intent on not fixing anything. That seems more like an indictment of the younger generations ability to get necessary things done.
Also, much of this trope compares the current situation of one generation against another. Rather than of each generation at similar ages.
When i was young we had awful landlords with horrid housing, rising interest rates, IMF bailouts, petrol price spiking and imminent rationing, and lots of strikes and general unrest. It looked bleak, and was for a long time.
Sound familiar??
But things changed over time and many prospered subsequently. It took a strong person to make the necessary changes, and also the good fortune of north sea oil, but it was a time when politicians had come from a life of actually doing jobs and running business etc. Since then I just see professional politicians who only know how to campaign and who, on achieving power, continue to campaign instead of being unpopular but governing wisely.