Again this is evaluating HW through a SW prism. Where’s github for bridge designers? rocket scientists? brain surgeons?
HW engineers share info in pretty much the same way that every other industry in the world does (except SW). The concepts are made available through patents, conferences, journals, and press releases. More detailed info is often made available through purchaseable IP.
Maybe it could be better, but there are good reasons that HW IP can’t be shared as easily as SW source code.