How long does Google send out their crawlers to a page that has been removed (i.e. a 404 error not found status)?

The simple answer, as mentioned in the thread is, forever.

Why does Google continue to try to access these pages?

Say you bought a domain name from someone and put up a new site. Say that Google refused to pick up your /about.html and /contact.html pages, and that eventually you found that it was all because once a page went 404 and Google refused to ever look at that URL again.

You would think that was a bad policy, so Google will continue to spider pages returning a 404 response.

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