Why are 301 redirects better than 302 redirects?

In a nutshell, 301 redirects are better for SEO because they definitely pass along link equity, whereas 302 redirects may not. Also, Google indexes the destination URL with a 301 redirect, with a 302 redirect Google will keep the original URL in the index and continue to recheck it.

What is a 301 redirect?

A 301 redirect indicates that a page has permanently moved to a new location, so link equity from the old URL is passed along to the new URL.

What is a 302 redirect?

A 302 redirect indicates that the page has moved to a new location, but only temporarily, so link equity from the old URL is not passed to the new URL, and the new destination URL is not indexed. It is appropriate to use a 302 redirect when the redirect is actually temporary and will be removed.

Additional information:

https://developers.google.com/search/docs/advanced/crawling/301-redirects