As an expert in the field of film and entertainment, I can provide insight into the reasons behind Spider-Man's absence from the early Avengers films.

Spider-Man, a character created by Marvel Comics, has been one of the most popular superheroes for decades. However, the rights to the character for film adaptations were not originally held by Marvel Studios. Instead, the rights were licensed to Sony Pictures Entertainment. This licensing agreement meant that while Marvel Studios could include Spider-Man in their cinematic universe, they did not have full control over the character's film appearances.

The first two Spider-Man films directed by Sam Raimi were produced by Sony and released in 2002 and 2004. After a couple of sequels, Sony rebooted the franchise with "The Amazing Spider-Man" in 2012, further complicating the character's integration into the Marvel Cinematic Universe (MCU).

However, in a landmark deal in 2015, Marvel Studios and Sony agreed to share Spider-Man's rights, allowing the character to appear in both standalone Spider-Man films produced by Sony and in the MCU. This is why Spider-Man, portrayed by Tom Holland, was able to make his first appearance in "Captain America: Civil War," which was released in 2016.

Before this agreement, Spider-Man could not appear in the Avengers films due to the legal and financial constraints of the licensing agreement between Marvel and Sony. The collaboration between the two studios was a significant step that allowed Spider-Man to join the Avengers and other Marvel heroes in subsequent films.

read more >>

Its just because spiderman's movie rights are with sony and rest of the characters are currently owned by marvel. So until or unless , marvel gets a deal with sony which highly unlikely you won't see spidey in avengers. Note: The answer justifies his absence from movies , I haven't read spiderman comics in detail .read more >>