ESBs gathered all control over the system in a single place: communication, schemas, orchestration, infrastructure. Over time, this revealed systemic issues:

• The ESB became a single point of failure: a bug could bring down entire system.
• ESB changes were risky and slow: engineers had to deeply understand schemas, adapters, business rules, and their interdependencies.
• Updates to services became problematic: even a small change in API required coordination with the ESB integration layer and orchestration logic.
• The ESB team turned into a bottleneck, struggling to catch up with changes in different services.
• Horizontal scaling was limited: ESBs commonly relied on vertical scaling and expensive hardware.

These issues slowed innovation and adaptability, turning large systems rigid, slow, and outdated. Another kind of architectural approach had to appear — one favoring independent ownership, decentralized control, and horizontal scaling of any service.