Even if you can get instant approval, Dell or HP won't Fedex you 50 servers next day like they will 50 laptops.
And once you're a customer you get to deal with sales channels full of quotes and useless meetings and specialists. You can't just order from the website.
You can get servers elsewhere as well and they can be more agile than Dell/ HPE/ SuperMicro/ Lenovo. Asus, Asrock, Gigabyte and some other brands can ship servers rather quickly. Perhaps not the next day but the prices are much lower out of the door especially if you are a smaller customer. Most companies know well in advance how much compute/ storage they will need. So if something takes a month or two it isn't a big issue.
And once you're a customer you get to deal with sales channels full of quotes and useless meetings and specialists. You can't just order from the website.