The average person buys a phone amortized at 36 months minus trade-in value. So they do indeed buy ram every month but it's a line item on a phone bill.

Assuming an 8GB phone on average and 2x16GB DDR5 desktop sticks being ~$400, the average person then buys 0.25GB RAM per month at $3.125.

If you want, you can add in a 16GB laptop every 36 months, tripling the total to 0.75GB and ~$10 a month. Still, that's multiple times less than the increase in egg price compared to the average consumption.