Socialism already does work. You can look to China, for example, to see its success in the modern era.

But, to answer the question more specifically, direct democracy on too large of a scale transforms into its opposite and becomes undemocratic.

The problem is that humans are not supernatural all-knowing beings. There are limitations to human knowledge, and it is not possible for a single person to know every intricate detail about a country with millions of people.

If you overwhelm people with requiring them to make decisions on things on too large of a scale, then what you always find is that most people will end up seeking an “understanding” of what they are voting on through popular media sources.

This is inherently problematic because it means people’s choices then are not something they come to organically decide upon through on-the-ground grassroots knowledge, but they become a decision made solely from consuming popular media, and so whoever controls the popular media ultimately will get to largely decide the outcome of the vote.

This is not a problem you can solve by just convincing people to do more research and vote smarter, because it is ultimately not a people problem but a logistics problem. If what you’re voting on isn’t something you have a deep pre-existing grassroots connection with, then you’re not going to know much about it at all unless some media infrastructure tells you about it, but then what you know about it will depend upon that media infrastructure, and what you know about it inherently will confine the possibilities for what you can vote on.

We see this even without direct democracy, just when elections for representatives are on too large of a scale. For example, in the USA, the mainstream media is privately owned, so if you want more representation in the media, you just have to spend more money. For large-scale elections like those for US Congress, most people don’t know the candidates through any grassroots means, but instead because they are told about them on television, and nobody is going to vote for someone they never heard of before, and so inherently this means that who people will vote for will depend upon who they saw on television, which depends upon who spent the most money on private media.

Hence, the person who raises the most money wins 91% of the time, and it is not like the other 9% are people who raised barely any money, but are pretty much always the person who raised the second most amount of money.

This, is, again, not a people problem. It is unfair to say that regular people are just “stupid” for not knowing better. You are requiring things of them that are just unreasonable, and, to some degree, physically impossible. Humans are not supernatural all-knowing beings, and these kinds of political systems with large-scale elections only serve to take advantage of their limitations in order to create an illusion of democracy, but a democracy that is easily puppeted by those who control resources as they can control what knowledge people have access to and thus frame the whole debate.

In most US presidential elections for example, there are usually more than 100 people, sometimes even more than 1000, who run for president, yet most people cannot name more than 2, and almost none can name more than 4. How can you know you are voting for the candidate who best represents you if you don’t even know who they are? Have you ever stopped to ask yourself why is it that the 2 you did know about were ones you knew about? How is it that the knowledge of those 2 actually entered your brain? It is because they are the ones with the most money and thus the largest media presence.

You have a “choice” between one candidate or the other that the television told you about, but ultimately, no matter which you pick, the television always wins. Or, to be more specific, those who control the media infrastructure, which ultimately comes back to those who control the means of production generally; i.e. the wealthy oligarchs who rule the society. You only are picking between their factions, and you have no possibility of ever escaping that.

This is something a lot of people struggle to understand. They think it is “democracy” just because they have a “choice.” But what they miss is the framing of those choices in the first place. Why are the two choices you are given the two choices you are given, and not some other two choices? Any tyrannical autocrat can give people “choices” that are just between two of their henchmen. Does that make it democratic? Obviously not, but for some reason, people struggle to apply this same reasoning when it comes to corporate oligarchies.

For democracy to actually represent the people’s interests, you have to take into account people’s limitations rather than abusing their limitations for faux democracy. Small scale grassroots elections where people can reasonably know who they are voting for through the grapevine without relying on the mainstream media. Those elected officials then have their own small scale elections to elect officials to even higher branches of government, and you repeat this a few times until you have formed your central government.

You can form a central government for a large country of hundreds of millions without any individual election ever exceeding tens of thousands of people, but with all elections ultimately originating from reducing down to a grassroots democratic election at the base.

You need representatives as a way to balance knowledge in society, to prevent a country from deteriorating into a dictatorship of the popular media. Honestly, most countries these days suffer from too little representation, not too much.