Subtitled episodes are frequently available within hours of broadcast while dubbed versions follow weeks or months later. The gap reflects the amount of separate production a dub requires.
Subtitling is translation, dubbing is production
Subtitles require translation, timing and a check, all of which can be done by a small team working directly from the episode.
A dub requires a script adapted for performance, a cast, a recording studio, a director and an engineer, with everyone scheduled together.
The second process involves far more people whose time has to be booked in advance, which is what introduces most of the delay.
The script has to be rewritten, not translated
Dialogue must fit the mouth movements already animated, which constrains syllable counts and phrasing in ways a subtitle never faces.
Adapters therefore rewrite lines to convey the meaning within those limits, which is slower and requires judgement about what can be lost.
Jokes and wordplay usually have to be rebuilt entirely, since a literal version will neither fit nor land.
Recording cannot start until the picture is locked
Performers record against finished animation, because timing depends on what is actually on screen rather than on a storyboard.
For a weekly series that material arrives close to broadcast, so the dub can only begin once the subtitled version is essentially ready to go out.
Any change to the picture after recording invalidates the affected lines, which is why studios wait rather than work in parallel.
Mixing is a second full pass
New dialogue has to be placed back into the soundtrack, balanced against music and effects, and matched to the acoustics of each scene.
This requires the original elements separated from the dialogue, which the rights holder has to supply and which is not always immediately available.
The mix is a technical stage in its own right and adds time after every line has been recorded.
Simultaneous dubs are possible but expensive
Some titles now release dubbed episodes close to broadcast by committing resources in advance and working to a compressed schedule.
That requires the production to supply material earlier and the dubbing studio to hold capacity open, both of which cost money.
It is reserved for series expected to reach a large audience, while everything else follows the normal sequence and arrives once the season is well underway.