Why does Аниме always have to have 26 episodes?

12-13 episodes:
One season (example: Spring)
(One season duration: 3 months, 1 episode per week = 13 episodes)

24-26 episodes:
Two seasons (example: Spring and Summer)
(2 Season duration: 6 months, 1 episode per week = 26 episodes)

How much is epsodes Аниме will have depends on creators.
If they decide to make the Аниме with 25 episodes, this Аниме continue through two seasons... (example: Spring and Summer)
It's rare that Аниме ended up in the middle of season (example: Summer)

Ps. Sorry for my english, but I hope this will help Ты :)

Good question,I have no idea,maybe to see if poeple see it,if they do they make more,that's what I think

IDK. It's usually the older animes like Trigun (I think it's a 2003 anime) that have 26 episodes. Actually, the older animes usually had 25 episodes. Trigun had 26. The newer animes are much longer, well, except for Kuroshitsuji. Altogether, it has 36 episodes. From what I've heard, One Piece has over 400 episodes. Bottom line: I have no idea why the episode limit. I've heard of short and sweet, but IDK if those same principles apply with anime.

because when famous Манга turns into Аниме it is only until half the story line it is the wraped up for 1 или 2 seasons for 24 или 26 episodes because Манга is not as Популярное as the Аниме however if the Аниме gets extremely Популярное it is then stretched like a rubber band to make money though that is my opinion.

Who сказал(-а) Аниме with 12-13 episodes only had 1 season? Koihime Musou has 13 episodes for each 3 seasons....
On Topic: I don't know the answer to that totaly wrong question...