And why would they do that? Zcash is a BTC clone, with an added ZK-snark sidechain. Bitcoin will add Zcash's tech as its own sidechain and Zcash will die. The only purpose Zcash serves is to fund the development of zero knowledge tech. It won't retain value long term.
ZCash is useless, bitcoin now has tumblebit technology, which will destroy all anon alts, bitcoin will have anon feature too