SCOTTSDALE, Ariz.—For years, credit unions have worried about deposit outflows to crypto exchanges, fintechs and online investment platforms.

But new research suggests they may be focusing on the wrong threat.

The bigger issue isn’t that members are buying Bitcoin or moving money into stablecoins. It’s that younger consumers increasingly view platforms such as Robinhood, SoFi, Coinbase, Fidelity and Schwab as their primary financial relationship—places where they can bank, invest, save, borrow and, increasingly, manage nearly every aspect of their financial lives.