The market cap of BTC currently it is round 250 billion USD. This is so much money, it is almost 100% sure, there will be someone, who can solve the “defi on BTC” challenge. The defi already growth 1500% in 2020. And the tokenized ERC20 wBTC token have more than 1 billion USD market cap right now.
Next to the tokenization, the other method for defi are the smart contracts, inegrated on the Bitcoin network. It is not simple, due the limited coding language, and the scaling issues. But the cryptoverse is growing day by day, so soon or later someone will figured out, how to doing this in usable, effective way.