I think JSGI was somewhat notable in the early days of Node.js until Connect became popular.
Connect is a middleware framework for node's http module and IIRC became the basis of Express (which is now entirely independent of Connect but remains compatible with Connect middleware). Express is (still) the most popular Node.js web framework.
I think the problem with JSGI is that it's not built into Node.js and the Node.js community tends to favour smaller, specialized libraries. JSGI just seems like an unnecessary layer of indirection from that point of view.
Connect is a middleware framework for node's http module and IIRC became the basis of Express (which is now entirely independent of Connect but remains compatible with Connect middleware). Express is (still) the most popular Node.js web framework.
I think the problem with JSGI is that it's not built into Node.js and the Node.js community tends to favour smaller, specialized libraries. JSGI just seems like an unnecessary layer of indirection from that point of view.