You don't even need 10k employees, I see it make sense with ~450 employees if you also have a decent IT team and funding. The issue is most companies can't see the need to keep things they own up to date - there's always a temptation to "just put it off a year" to make the budgets look better, till they hit near catastrophe with being 5+ years beyond reasonable. The cloud "forces" them to put in update, maintenance, employee overhead etc up front and forever. They just pay a premium for that service IMO.

I used to think it was kind of stupid, but then I realized - companies hire consultants at exorbitant rates to help them do things they don't have the in house skills for - so really - building that into the overall cost might still be a wash. The expensive part of Cloud IMO turns out to be needing training, consultants or new employees with different skills to manage it, which all charge more than traditional on prem because cloud is still the current ?fad?. And the unseen costs of screw ups by the cloud provider themselves losing data, being down, or having a security breach that affects you - and you're completely out of the picture with remediation or even knowing what might be a risk.