What do you mean by already exist? It didn't exist when they allocated the budget before production.In what way does these require a $10 upgrade when they already exist?
For your typical remastered re-release - like the Skyrim Special Edition, The Last of Us Remastered, Metro Redux, Homeworld Remastered, and so on - additional work was added to the game that did not exist when the game was originally made. That's why there's a price tag. When Spider-man Mile Morales was released... it had everything in it already. They didn't revisit the game and add in things that didn't exist - the "enhancements" you're speaking of aren't enhancements at all, they're the stock-standard features that were budgeted and paid for by the development that goes into the sticker price PlayStation gamers already paid when they bought the game. In what world should anyone pay more for features that already exist in the product they already paid for? Madness.
Except that they're not? Every announced game available from Microsoft for the Xbox Series X is priced AUD$100.00 (USD$60.00) or less. Every first party game announced by Sony for the PS5 is AUD$125.00 (USD$70.00). Even the cross-gen ones. Halo Infinite? AUD$100.00. Forza Horizon 5? AUD$100.00. Psychonauts 2 (On PS4 or Xbox)? AUD$100.00. As of today, I believe the only publisher besides Sony to commit to a complete transition to USD$70.00 pricing is Activision - although I have missed some press releases, so that may no longer be accurate. To date, everyone else has been doing it on a game-by-game basis to test the waters.