Performance art (in general) is an enacted work of art that takes place over time (and perhaps a social layer). Other types of performance include music, dance, theater, etc … all these art forms are happily reproduced. Everyone realizes that the reproduction is nothing like experiencing the original.
Further, even without the dimension of time, the same can be said for material objects. Experiencing a material art object is a fleeting, lived experience that no jpg can reproduce. When Tino Sehgal (or any artist) takes the position that their artwork cannot be photographed because it contains something that other artworks don’t, they insult everyone (as if other artwork can safely be photographed without much loss).