That’s a fair point.
The differential here is actually the cost of operating Roblox as a service, and matches how Roblox reports the % of earnings going to creators overall. The DevEx rate bundles in costs of server hosting, database, infrastructure, maintenance, app store fees, employee wages, etc etc, all into one rate that doesn’t expose the costs directly. That’s why they’re different.
In practice, this actually turns into a subsidy for newer creators. The more you earn, the greater the costs you pay, which then lets Roblox offer free services to newer creators.