1/ General purpose models are still not good at this task. I would personally love it if I could trust my agent when it says its done after a 24h build. But whether it's because of sycophancy, context degradation over time, or something else coding agents still struggle to verify their own work. Maybe with 1B context windows this will change.
2/ Infra is still annoying to setup. We wanted to provide a unified interface across web, mobile and soon desktop as well. So users don't have to worry about provisioning, concurrency, security, etc.
3/ As with any SaaS, even beyond the initial build, maintenance is a headache. I think most companies would rather not consider agentic QA as one of their core competencies and investments. It takes a ton of eng effort to keep the lights on, continually update the models used, train new ones, groom ground truth, onboard infra providers, etc.
This strikes me as a company that is late delivering a product for November 2025, when it is November 2026.
But I would say even for medium sized features, it's the same difference between asking your Codex to "review the code make no mistakes" and using a paid AI code review tool.
As your product surface area increases, you need fundamentally different agent architecture to maintain context over time and across bug bash sessions. The benchmark apps are probably among the simplest apps we test on, and even those show a massive perf. gain. For large companies with 1000s of important user flows, have to support different viewports, and need to work across mobile/web/desktop, asking Codex to test it all before a big launch is not scalable.
Even basic constraints like the # of browsers/devices you can run concurrently, the amount of reliable TPM you need, and how many agents can run on a single box become problematic. You also have to think about ktlo: how do you evaluate new model releases in a data driven way, how does agent become more efficient itself over time, etc.