At a previous job we had some decent on prem resources for internal services. The SRE guys had a bunch of extra compute and you would put in a ticket for a certain amount of resources (2 cpu, SSD, 8GB memory x2 on different hosts). There wasn’t a massive amount of variability between the hardware, and you just requested resources to be allocated from a bunch of hypervisors. Turnaround time was about 3 days too. Except, you were t required to be self sufficient in AWS terminology to request exactly what you needed .
Now imagine having to deal with procurement to purchase hardware for your needs. 6 months later you have a server. Oh you need a SAN for object storage? There goes another 6 months.