Imagine that a whole nation's statute laws, and associated common laws, were frozen in time for over a thousand years, because (the statutes were declared to be immutable canon, and) any judges with sufficient authority to strike out old common law and to establish new common law were long gone. That's Judaism (specifically the Talmud)! (Speaking from experience as a Jew.)

The "eruv" definition was established back when the biggest conceivable area that it might cover was that of a medieval village or ghetto, of maximum several hundred (small cramped) houses, i.e. let's say about the area of Vatican City, which is 0.49km2 (0.19 sq mi). Whereas the total area of Manhattan island is 59km2 (22.7 sq mi). So, yes, in my opinion, a Talmudic judge would consider the modern-day Manhattan eruv a gross perversion of the spirit of the law, and would update the definition accordingly. But no such judge exists in this era. So, yay, let's play "how ridiculously can we apply anachronistic archaic rules to the modern world" - apparently, ultra-orthodox Jews consider it such a fun game, that they let it rule their entire life!