Many other blockchains were or are now just as good for DeFi as Ethereum. Or at least close enough. There's quite a competition there you seem to have missed out completely.
I don't see a good reason for Bitcoin care at all about this and I think that Bitcoin side chains has lost the train for this.
So it's imho it's closer to "failed experiment", although it's not even known enough to be called like that by such a number so it would matter...
But don't worry. I am not convinced that DeFi does indeed worth the hassle...
One thing for sure is that Bitcoin is not good for everything. It works great as a store of value, but it's terrible as "digital cash" for day-to-day payments. The contrary happens with Ethereum. It's best to leave the Bitcoin network as is in order to ensure its decentralization, security, and reliability. Making it more complex, will only make matters worse in the long run. Imagine if Bitcoin was an AIO (All-in-One) blockchain network capable of handling anything in its path. It would bring many unnecessary security risks in the long run. It's best to keep it simple, while letting alternative blockchain networks serve their unique purpose in the mainstream world.
For now, "De-Fi" on Bitcoin remains as an experiment. With ETH's rising popularity, I doubt people will adopt Bitcoin for "De-Fi" in the future. Sidechains providing smart contract features for Bitcoin will only remain as an alternative than a replacement to Ethereum. I don't mind about this, as long as, both projects work together (BTC and ETH) in order to make crypto land a better place. The wide variety of cryptocurrencies to choose from, gives people a choice to select from one coin to another depending on their daily needs. Ethereum will always be the "King of De-Fi" because of the many dApps built on it over the years. The world's second-largest cryptocurrency by market cap has a lot of developers and individuals supporting it, becoming a place of attraction for new "De-Fi" projects. Even with competing smart contract platforms (like TRON, EOS, and Cardano), Ethereum has remained as the leading platform for "De-Fi". Bitcoin is better suited as a store of value than anything else. Time will tell us what Bitcoin's use cases will be as the network maintains active development and innovation. Just my thoughts