Let's take a concrete example. Suppose that class warfare rhetoric utterly wins, and as its first scalp The People decide that the filthy rich Bill Gates needs to have 100% of his wealth confiscated for the good of The People. For simplicity, let's assume that 100% of his wealth is in Microsoft stock. So, The People United take all of his stuff. What do they get? Well, they don't several billion dollars. They get "several billion dollar's worth" of Microsoft stock. Well... that didn't accomplish much. We can't clothe or feed the people Microsoft stock. We need to liquidate it into money to get anywhere, and The People aren't too happy about the filthy capitalist stench of suddenly owning that much stock anyhow, so they immediately sell it all. Of course, dumping all that stock on the market at once immediately sends the price plunging; depending on how foolish The People in terms of wanting to be rid of it immediately it could well plunge to nearly zero. The People destroyed billions of dollars of wealth to obtain probably hundreds of millions of dollars, and quite possibly destroyed Microsoft in the process, hardly a net gain. The stock was as valuable as it was partially because it was in Bill Gates' hands.
In practice, you can't just "claw" wealth from the wealthy and hand it to "the poor" and have the effect you're expecting. You can certainly destroy large amounts of wealth, and yes, the poor will come away with something, but it's far less efficient than the "it's all just money" model leads you to believe. You aren't taking "$100 dollars" away from the wealthy and giving "$100 dollars" to the poor; at scale, you're moving a $100 asset out of the hands of "the wealthy" and into the hands of "the poor", and that's not going to produce the results you were looking for. And again, let me emphasize, it does work to an extent, it just doesn't work as well as you might naively think.
Politics being what they are, people are going to assume that I'm a fan of this truth because I'm saying it. I'm not. It would actually be really cool if redistribution worked as easily as people thought it does! I mean, seriously, awesome. How wonderful it would be if equality could be engineered so trivially! And let me be clear, no sarcasm there. However, it is still true, and it is something we ignore at our own peril. Also, does that mean all our social engineering schemes are hopeless? Well, no, again regardless of whether I'm a fan of them or not, but it does mean that, again, it's harder than we'd like to produce the results we're looking for, and it's a lot easier to overestimate the benefit to the poor and underestimate the damage to the wealthy and the general societal wealth (and even if you don't really care about the wealthy, you ought to care about the general societal wealth) that such schemes can have.