Homie's flat fee for sellers is dramatically higher than OP's, and the seller still pays a regular commission for the buyer agent (even if the buyer is using Homie as their buyer agent):
The higher fee means they can actually pay for all the costs they incur and still remain profitable. Including the buyer agent fee means that they're in a position to attract non-Homie buyer agents to the platform, so they're not trying to bootstrap a market from scratch. It also means they can give half of that portion of the fee back to the buyer as an incentive to choose Homie, whereas in OP's model there's no reason for buyers to choose them.
Sellers Pricing: https://homie.com/pricing#buy-sell-tabs-first
Buyers Pricing: https://homie.com/pricing#buy-sell-tabs-second
The higher fee means they can actually pay for all the costs they incur and still remain profitable. Including the buyer agent fee means that they're in a position to attract non-Homie buyer agents to the platform, so they're not trying to bootstrap a market from scratch. It also means they can give half of that portion of the fee back to the buyer as an incentive to choose Homie, whereas in OP's model there's no reason for buyers to choose them.