Unless their venture capital backers want to pony up endless infusions of capital, most robo-advisors are more unsustainable than ever, according to Ric Edelman, chairman and founder of Edelman Financial Services.

Many are struggling to “make payroll,” and their best hope is to be acquired, Edelman said. Indeed, that has been the preferred exit strategy of many robo-advisors.

BlackRock acquired Future Advisor and Invesco acquired Jemstep, reportedly for healthy prices. Both asset management complexes said they bought the platforms primarily to help financial advisors work with smaller clients, not to attract do-it-yourself investors.

It wasn’t supposed to turn out this way. Speaking at a Money Management Institute conference in October 2015, Adam Schneider, principal at Deloitte Consulting, speculated robo-advisors might initiate truly disruptive strategies and start playing hardball.

“ETFs, online brokerage, 401(k) plans and electronic payments all grew very slowly for a while and then took off,” he said.

That scenario is still conceivable, but it looks less likely. In the last 18 months, the big winners have been financial services giants.

Schwab and Vanguard got into the business relatively late in the game; Vanguard now reportedly has about $50 billion in assets under management and Schwab Intelligent Portfolios had about $10 billion. In contrast, Betterment, which has overtaken Wealthfront as the biggest robo-advisor, reportedly had about $8 billion. Both firms have started to hire real human financial advisors, though it remains to be seen what role they will play.

But Edelman maintains that even businesses like Betterment and Wealthfront are not viable, going concerns as long as they keep charging miniscule basis points. When competing against giants like Vanguard and Schwab, both of which can subsidize their own robo vehicles indefinitely, the model makes no sense.

In a world where giant players are slashing fees to near zero, using price as the main value proposition makes it very hard to differentiate an offering. Edelman’s own robo advisor, Edelman Online, starts with the same fee schedule, $100 for a $5,000 investment, as the firm's main business. It has attracted 998 clients with $61.8 million, or just under $62,000 per account, and the average client 54 years old. The technology investments Edelman has made in its nascent robo advisor are also being used for clients on its primary platform.

Edelman considers Personal Capital, which doesn’t view itself as a pure robo, a more viable model. Personal Capital charges 90 basis points.

“The higher the fee, the greater the viability,” Edelman says. Personal Capital has “CFPs providing advice and service, not just algorithms.”

It’s also worth noting that, while many start-ups don’t make it, others eventually succeed, but in a very different business than they expected at the beginning. The first robo-advisor, Financial Engines, spent the better part of a decade searching for a real business before striking it big in the 401(k) consulting business. With trillions in unmanaged assets, the 401(k) market remains ripe for both human and robo-advisors.

Financial Engines had one other advantage. Its founder and chairman in the early years was Nobel Laureate William Sharpe, a distinguished Stanford University professor. The venture capital community is overpopulated with alumni from Stanford where, by all accounts, Sharpe was universally beloved by his students.