Why would you think that? Short seasons are all the rage these days with prestige shows.
Game of Thrones has 10-episode seasons as a rule, and its latest season was only 7 episodes.
Westworld,
The Man in the High Castle, and
The Handmaid's Tale have 10-episode seasons (as does
Killjoys on Syfy).
American Gods' first season was only 8 episodes. Shorter seasons are popular because they're basically miniseries, extended movies that let producers craft a tighter narrative with less filler, as well as being able to invest more money in each individual episode and thus improve quality.
http://www.vulture.com/2015/06/10-episodes-is-the-new-13-was-the-new-22.html
In any case, the package of shows that Marvel Studios developed back in 2013 was always conceived as 60 episodes, comprising four 13-episode series and an 8-episode crossover miniseries. That was the plan before Netflix even bought it.
http://deadline.com/2013/10/marvel-...-series-a-mini-for-vod-cable-networks-611826/