Why is options.animated=true not the default?

## Question about an existing feature
I had a rather frustrating user experience, because why would anyone input a gif and expect it **not** to read all animated frames? I find this rather unintuitive and would like to suggest options.animated=true as the default.

Related: https://github.com/lovell/sharp/issues/3625

Start with the options.animated behavior described in the issue and review related issue #3625 to understand the existing rationale. Then locate where this default is defined and determine the compatibility implications; done requires a maintainer-backed decision on whether the default should change and what behavior should be documented.

Written by the indexing model from the issue text.