I can't speak to this particular case, but most of the delay is likely to be organisational rather than technical at this kind of scale.

Don't think about how hard it is to migrate a VM to a new provider. Think about how hard it is to:

* Get procurement to sign off on a new vendor

* Guarantee that your ISO compliance standards can be met under the new regime

* Make sure that GDPR requirements are met during any data transfer process to the satisfaction of your legal team

* Get the old infrastructure team and the new infrastructure team coordinated enough to be able to plan a migration without downtime

* Mollify the consultants that the CEO's friend said he should hire

* Analyse the migration plan to death to derisk it while at the same time be unable to actually evaluate it small scale due to the points above

Don't forget any relevant training for employees (e.x. for things like 'how to connect to a virtual desktop'). That can add up in some cases.