They like it just as any other arbitrary meta tag.

Only meta's with HTTP-EQUIV attribute are more or less universally recognized, but they must not conflict actual server headers but rather complement them.
Meta data with 'NAME=' attribute are custom/arbitrary ones and some of them are recognized, some not, by different browsers/robots.
E.g. Google introduced '<META NAME="GOOGLEBOT" CONTENT="NOODP">' meta tag only for their bot, which may(not) be understood/accepted by others.
Any unknown meta tag is simply ignored.

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Impossible? You just underestimate the time.