Those costs are never taken into account. It's always the "low" price of licensing/use/dev that is looked at, and then... you have the regret phase. Which never end because "we already invested so much", and the famous "in the long run it will be cheap... oh wait, we have a newer offer"
How long ago was that a thing? I got in in the 2000s and there was only a single email system for the entire Army. 10 years ago they moved the whole DoD to DEE.
As an employee of a company where about 1/3 of our workforce have migrated to Google Workspace and the rest have not, I have a (pretty long) list of things that are a pain. Anything to do with sharing is awkward. Google Chat vs Teams is a headache. Lack of calendar integration is annoying.
Obviously YMMV, but I don't think it's as simple as you're making it out to be.
How do your Office users share files? At a previous employer they refused to migrate away from an ancient companywide network share, combined with people emailing each other QuarterlyReportQ42021_final_Fixed (7).docx. There was absolutely no interest from IT (which the company had recently outsourced) to actually facilitate migrating to a sane sharing model a la Office 365.
OneDrive. Enterprise deployments have something similar to consumer-grade OneDrive, but more enterprisey with compliance controls built in. And of course all the regular Office apps work well with it — it’s not just browser based.
It’s honestly pretty good. All the usual features are there — importantly, version history (no more Contract v15 FINAL.docx).
The key thing is it works with Teams and SharePoint and has collaborative editing, works in browser, desktop app, or phone.
They had an on-premises version of OneDrive too, not sure if that’s still a thing.
It’s not all a bed of roses. Gmail still feels nicer than Outlook web, but Outlook web is catching up. Collaborative editing feels much more robust in Google Docs. But the OneDrive client is way nicer than Google Drive (for me, at least).
I’d definitely say Google’s and Microsoft’s “online business collaboration” offerings are comparable. I suspect users will have preferences based on what they’re used to.
Of course, if your org uses both you’re in for a world of hurt. Email works well enough, but even calendaring has friction. Filesharing / chatrooms? Doesn’t interoperate well at all.
Which neither side supports fully. So now you're paying a software dev to integrate the two. And of course, they're not going to get recurring events implemented correctly, especially when some events are exceptions due to holidays or other scheduling conflicts.