> "the internal IT of a company"

Many small and medium companies don't have any internal IT. Maybe the original parent commentor works for an MSP / outsourced IT services provider / as an IT consultant.

> "What could be so complicated that"

Windows 11 has hardware requirements that Windows 10 didn't, their equipment may need to be reviewed/audited or refreshed - planned, budgetted, quoted, ordered, received, checked, configured, user data migrated over for dozens of devices. Business customers need to buy Windows Pro not Windows Home - and need enough IT experience to know that, non-technical companies may have bought some Windows 11, had problems, and needed to call someone for help. A company might have some internal IT who could do it, but are busy with other projects and don't have time to plan and execute an upgrade. Windows 11 comes with new Group Policy templates which need importing to a Windows domain and configuring - and may need reviewing or auditing for regulatory compliance to see what needs setting up and the parent commentor is some kind of compliance person helping with paperwork instead of a technical person. A company might take an upgrade to Windows 11 as a time to change other things like a move to Microsoft Cloud Services (OneDrive, Microsoft account for login) and each user needs to be given a new laptop and have all their settings moved over. A company might have specialist software from vendors who aren't very progressive - e.g. optician's software which manages retina scanning cameras - and needs lots of time consuming hand holding with the vendor support line before the vendor will agree to the move, even if it would in principle work fine. Regardless of technical issues, the upgrade could take an hour or two per machine, over dozens or hundreds of machines, that's either a big interruption which needs planning (staged rollout for different departments, say) or needs some automated way to deploy it which needs setting up, testing, and checking on, and may just hire some temporary contractors for more people to do that. There may be users who could do it, but won't because it isn't their job, or aren't allowed to by their manager or union so it isn't their responsibility if it goes wrong.