Unlike Steam keys, there are no ways to distribute Playstation keys outside of Playstation platform. By removing retailers and second hand markets, what exactly would make Sony or any other publishers to continue offering any deep discounts on their products on a closed platform, especially when their biggest competitor Xbox has dropped the ball heavily.

I constantly rotate physical games for my PS5.

I'm in the UK, and CeX is a great shop to trade in a game for store credit once I'm finished with it, then pickup whatever I want to play next. Most of the time I can completely cover the cost of the next game with the credit received from the trade, or use some store credit leftover from a previous visit!

When a Sony studio Insomniac Games were hacked and a lot of internal documents were leaked, there were statistics for Sony's first party titles and their sales stats and what the split was between physical and digital sales[0] and for some of the titles, they sold mostly physical compared to digital. Apologies for poor quality, couldn't find a better image

[0] - https://imgur.com/lDhRmUh

Due to the steam sales and deep discounting its easy to buy games on steam for much cheaper then the consoles. For console where a game may be £60 for several years, buying physical means you can resell. For anyone with a budget, it makes a huge difference on how many games you can play.