Why are the costumes in comics and movie adaptations not the same? [duplicate]

You're asking a question of why visual decisions were made when adapting and remediating a character. The most obvious if unhelpful answer is because someone chose to change it.

it kind of starts and ends there really; it was a choice, and questioning that choice can only be answered comprehensively by said person that chose to remove the costume.

The picture you include in you question is not actually Wolverine's most common costume (if we accept that the black stripes down the shoulders/across the chests is his 'classic' appearance), which just goes to show how many variations there are.

In the case of Wolverine, we can speculate quite confidently that this decision was made because, tonally, the costume wouldn't fit with the rest of the film. Cyclops' line 'What would you prefer? Yellow spandex?' is a direct reference to how absurd the costume would look compared to the leather costumes worn by the X-men in the film.

Lastly, whilst you may be correct in stating that Wolverine's yellow and blue costume is 'iconic', it's not his only costume, and it has changed several times over since his first appearance back in 1974. Below are just a handful of the changes that have been made to his appearance since that date.

Variations range from subtle to extreme, but the point is there is no canonically accepted 'norm' for Wolverine's appearance.