Although the term sounds enterprise-heavy, the problem exists in SMBs too. A small business may still have a CRM, website forms, email, calendar, payment system, project management tool, helpdesk, and reporting dashboard that do not talk to each other well.
AI agent systems depend on application integration because agents need access to the systems where work happens. The stronger the integration layer, the more useful the agent becomes. Without integration, the agent becomes another isolated window asking humans to copy and paste things.