One reason historically was that the knuckle on the price curve shifted between the time the machine was released and when you upgraded. When a new generation of RAM came on the market, prices often fell rapidly as the process matured and competition set in.

This also played into sale or discount strategies: if the same model becomes cheaper over time but list pricing doesn’t adjust, you’re making a good bit more from everyone who isn’t price sensitive even if you allow resellers to discount it periodically or offer better pricing to business orders (“free RAM upgrade”).

Because that is how the business model works: You have the entry model to create a customer. Then those who really need more, are gonna pay substantially more. See basically every SaaS product.