Some anime have a lot of hype behind them for one reason or another, sometimes even before they've aired a single episode. The best of them manage to live up to those lofty expectations, but sadly, not all do. There are many ways an anime can underperform, but surprisingly, there are many that manage to get a hefty episode count under their belts.
Source:https://www.cbr.com/disappointing-anime-with-the-most-episodes/