It's all about reduction of surface and giving plugins access to the least amount of info. You expect a linter to only have (read) access to the code it lints. It shouldn't be able to modify files, it shouldn't have network access etc. WASI has a pluggable capability-based security system.

Some advanced linters might want network access but you can show this to the user, so they can make an informed decision about whether to trust that linter and their author with this power.

This isn't airtight security to protect against obviously-malicious authors. This is about creating a system that can deal with the reality that "trust" in an app store entails "a million shades of gray". I might trust a plugin enough to check for errors in my code, but not enough to actually modify my code.