One of the main reasons Netflix seasons are short is because they don't have a schedule to fill like a TV network. This is often an advantage, as show creators aren't forced to drag stories out and cram in filler episodes. Stranger Things is a prime example of this working well: with just eight-episode seasons, they're able to weave a concise but compelling narrative. So why do Marvel's Netflix shows have 13 episodes?
While some of the best original Netflix shows indeed share this (seemingly arbitrary) formula with the Marvel shows, the ones freed from this constraint are often much better off for it. That's not to say that a 13-episode requirement guarantees a bad show - the people at Netflix have proven themselves capable of producing high quality content, even in this format.
But this rigid restriction causes serious problems from a storytelling standpoint, especially when the stories are somewhat predetermined, as is the case with comic book adaptations. Marvel's Netflix shows occupy an interesting space in the complete history of the Marvel Cinematic Universe, and constraining their scope in this specific way can lead to a lot of issues. What follows is an exploration of why Marvel's Netflix shows have 13-episode seasons, and how they're harmed by this structure (plus a fair amount of spoilers).