Why does 410 deindex faster than 404?

Google interprets 410 as a definitive signal. 404 is treated as possibly-temporary, so Google retries for weeks before removing the URL. 410 says "stop crawling immediately".

Should I use 410 for deleted user profiles?

Yes if you want them deindexed quickly. Pair with a brief explanation page (in the body) for human visitors.

410 Gone: HTTP Status Code Meaning, Causes, and Fixes

What 410 Gone means

410 Gone is the more honest version of 404. Where 404 means "not found" (with no statement about why), 410 specifically means "this resource existed, was intentionally removed, and will not come back". Search engines treat 410 differently than 404: a 410 page is removed from the index faster than a 404 (which Google retries for weeks before giving up). Use 410 when you delete something permanently and want it removed from search results promptly.

When servers should return it: Return 410 when a resource has been permanently deleted and you do not plan to bring it back. For unknown URLs, use 404.

Example response

curl -i https://example.com/old-page

HTTP/2 410
content-type: text/html
<html><body>This page is permanently gone.</body></html>

More references

For a one-page reference of all HTTP status codes, see the HTTP cheat sheet. For testing API responses, try the API Tester tool. For inspecting responses on the command line, the curl cheat sheet covers the most common flags.