system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does it take years to make a single 1.5 hr film but HBO can create hour long episodes that air week after week?
gpt
A movie typically shoots for 30 days. The 6-18 month period prior to this is called the 'pre-production' phase and involves not just writing but casting, booking directors, booking editors, booking DOPs, rehearsals, location scouting, costume design, set dressing and construction, etc. Then there's the short production phase, and then you enter post-production where you do the offline edit, online, VFX, and ultimately lock for release. This period can last 6 months itself. 

All of these phases are drastically shortened on a TV show.

On a TV show, you still have to cast, book directors, editors, DOPs, build the sets, etc. But you only have to do those things *once*. You keep those people on staff, you keep the sets you built, you keep the cast. 90% of pre-production work is eliminated for every episode beyond the first. 

Rehearsals are shortened, too. The actors learn their characters, their mannerisms, accents, attitudes, they start to get the comedic timing of the show and their co-stars. Of course, they still have to rehearse scenes and learn their lines -- but TV rehearsals quickly become far more streamlined, quick, and low-stress compared to movie rehearsals where the director is carefully watching everything and making adjustments so the actors "get" the movie and their character.

This is true for other staff, too. Writers, editors, and DOPs all get into the swing of things after a few episodes, they learn the show's style and format, and they can work faster with less supervision.

On top of all this, TV shows aren't actually producing episodes week to week. Shows typically run year-round, and actors will be shooting scenes months before they air on TV. A show might run 16 episodes but be in production 50 weeks of the year. 

And then add one more factor: multiple teams working side-by-side. American TV shows don't just have one writer and one director, they have many. Breaking Bad was written by 10 people and directed by 25. Each writer can work on scripts separately and simultaneously, and 2 or 3 directors can be making episodes at the same time. Obviously this doesn't happen for movies. (Movies do often have a 'second unit' with its own director shooting scenes separate from the main director, but this is almost always just minor stuff like exterior/establishing shots, plates, and special stuff like the news-show segments from House of Cards.)