They thrive on mass producing a fixed set of products. Those products are ETFs, Mutual Funds... or in Wealthfront's case... a rebalancing strategy based on a 1960's white paper called Modern Portfolio Theory.
Each of these players spends a ton trying to mass market these products. You have financial advisors pitching mutual funds, asset managers shilling the virtue of their shiny new ESG ETFs... and robo-advisors all promising a set-it-and-forget-it panacea. Wealthfront got commoditized. Betterment at first... but then the discount brokers came in (Vanguard, Fidelity, etc) and just had a much more effective channel (advisors!) to the end investor. If you are just selling a singular product and that product is successful, you are going to get copied and beaten by competitors with better marketing channels.
Wall Street will some day transform from an analog industry of mass production to a digital one of mass personalization. The building blocks for said transformation are slowly becoming ubiquitous (fractional shares support, commission free trading, etc). Super excited to watch this happen.