Gotta be economics of scale and disc media. Cartridges and older media were much more expensive by comparison and had limited production runs.

Suddenly compact disc comes along and dozens of manufacturers are printing them for pennies at a time with production lines that could scale up or down as you required.

The readers and the tech behind them was ubiquitous and even for the added complexity, you only needed one disk reader on each console, whereas carts had a bunch of redundant hardware that had to be copied for thousands upon thousands of copies.

Now digital copies are even cheaper, and disk drives are less space and speed efficient so print runs are scaling down and manufacturers are charging more. All the while, physical access to software has tangible downsides to publishers such as sharing games and making copies (since drives are, again, ubiquitous) so they're frontloading the price of physical games to offset this reality.

Games sold for the most part. Baldur's Gate 1 sold 2.2 million copies over 5 years, Baldur's Gate 3 sold that during early access and over 10 million in less than a year. First Call of Duty sold 5 millions while the newer ones sell 30 millions. OG resident evil 2.7 million, newest resident evil 10 millions.

Once you've made a game the cost of producing another copy is pretty much just the cost of the physical disk and shipping and distribution. Like the biggest cost is labor from developers but once it's made you can and should makes as many copies as possible.

I'm sure there are a lot of factors, but shifting away from cartridges was a big cost cut.

most likely RAM/ROM prices at the time (probably a natural disaster caused a shortage that screwed anyone not using CDs like PS/PS2). Also CDs were significantly cheaper even if there were no supply chain issues. I actually think most games were sold for $50 USD, it's just that the outliers that cost more are a mix of first party games and games where at least the publishers thought they were better than everyone else.