It failed because overhyped chains such as Solana and TON took over the world by storm. Polkadot had good tech and vision, but without hype, it's doomed. Investors these days aren't looking for quality projects that are meant to stand the test of time (except Bitcoin and Ethereum). They just want to buy the next big thing that will make them a quick buck. Even if such project is centralized and unreliable.

Zcash was another good project. But where is it now? Long lost and forgotten due the lack of hype/excitement. I seriously doubt DOT will be able to rise from the ground up. But who knows? Crypto land often behaves in many strange and bizarre ways. So I'd expect the unexpected. Someday Polkadot will shine until it goes all the way towards the top 10 coins by market cap. I'd buy a few coins just in case...