It's CapEx vs OpEx.. this is why cost-benefit analyses should be a required exercise before seeking a cloud solution. There are myriad of other things that should happen as a pre-cursor as well, but I preach this shit ad-nauseum everyday to my leadership and to business owners. First it was all the rage for on-prem, then it's was full cloud, then hybrid, now cloud divestment. The wheel will turn another 180 in 2 years
Wasn't the cloud about off-site, redundancy, and scalability? Having non-redundant servers in one location is cheaper if you have the place and connections for them.
Yes, and then some. NIST 800-145 basically defines cloud as scalable, ubiquitous access to network resources (in addition to the 5 characteristics). That said, cloud typically carries 4 defined (or recognized) deployment models: private, public, hybrid, and community. Technically any deployment model can be on or off-prem which brings us to defining capital expense vs operating expense - do we buy the physical boxes and infrastructure, plus FTE to configure and maintain or do we just 'rent' space and scale as we need. The Total Cost of Ownership (TCO) really needs to be defined to know what is better aligned with the goals of the organization.
That said, if you host everything on-prem, best to have a off-prem cloud backup for BCDR (business continuity/disaster recovery) and if we host everything in an off-prem cloud, best to have a backup in a separate cloud in a different availability zone - TCO can get really tedious really quick.
Good points about TCO being something a company needs to assess for themselves, rather than "cloud is always cheaper" or "on-site is always cheaper". It's not my field but I'd hope there are approaches that let a company first use the cloud to figure out how much they really need, then later switch to on-premises and not have to reconfigure things (i.e. they can have their machines present the same cloud interface).