Any third party can robo-copy it and tell anyone how their portfolio should look like.
Also index funds in crypto does not mean the same as in stocks, there is extremely high systemic risk and negative correlations between coins.
These are some weird times.
I'm guessing its a user acquisition tactic for people who traditionally invest in mutual funds, ETFs, etc. this way they feel like they "understand" what they're buying into instead of actually needing to suffer through the learning curve of how blockchain works.
That is a major incentives no-no. Coinbase can make more money pumping coins into the index than managing the index itself. If I wanted and index'd solution for crypto, I would not use one like this.