Why does the inscription on a local bench read "To those who shall sit here..."?

{The bench is located in New York state, and it dates to the 1890s.) When I was taught the shall/will distinction, I was told that in the case of the third-person plural ( those ), the use of will indicates simple futurity whereas shall indicates intent on the speaker's part. Shouldn't it be "To those who will sit here...", given the speaker has no control of, or designs on, the sitting?