— But why not go in this direction? viz.: We derive something (loans), which obtains both in Eretz Yisrael and outside of it from something (Hebrew man-servant), which obtains both in Eretz Yisrael and outside of it, and this is not to be refuted by land-shemitah, which obtains only in Eretz Yisrael.
It is, therefore, written "seven years" (here) - "seven years" (in respect to land-shemitah) for a gezeirah shavah (identity): Just as the seven years of (land-) shemitah are universal, (and not individual), so, the seven years of loan (-shemitah) are universal.