Just because some political ideologies have their day, doesn't mean they all will. Representative democracies of the 19th century had been preceded by proto-representative democracies like the Parliament of England, they weren't a fully new thing at that point by any means, even at the large state level: https://en.wikipedia.org/wiki/Parliament_of_England

There have been attempts at large, nation-scale anarchist communities, like revolutionary Catalonia, or Makhnovia, but the most fundamental problem they have isn't functioning well, but simply continuing to exist. Without a strong state, they seem to just fall over to competing states or forces. And this isn't very easily fixed within anarchism, because the whole point is to not have a state, and certainly not a strong one.

The most fundamental flaw for a large anarchist, state-equivalent community, is the inability to resist state or state-like forces both internally (revolution/civil war) and externally (other states invading or taking territory). While certainly anarchists theorycraft on how this issue can be fixed, out in the real world, well, it hasn't happened yet, so it remains theorycraft.

Even some of the real-life examples anarchists point to, like Rojava, aren't really very anarchist; Rojava still has plenty of police, for example, which is a very un-anarchist thing to have around.