Years ago they did. It was called the "Mac Cam". Now it's ball calls not foot faults.
The call — foot-fault - is made so rarely that the networks don't even think about putting a camera to cover the line. Entire tournaments go by without a single foot-fault call in any match.
That;s why the line judge should have NEVER made that call unless it was an egregious foot-all-over-the-line situation, which it was not.