I've asked here before about confidential TXs, Pederson commitments,...etc and how the fee is determined
People answered they don't know of a real implementation
I found them in almost every Blockchain course even MIT that was mainly about Bitcoin with a very little Ethereum.
And also this paper that mentioned Bitcoin explicitly and my same question about how do we know the fee? (Although didn't directly answer it)
https://youtu.be/Adrh6BCc_Ao

Then I found out it's a sure thing that they're not really implemented.

So, why no one simply implemented them (I mean by suggesting a BIP) through a flag bit (like HTCL if I remember correctly) that changes the TX format where UTXOs are encrypted, only the fee is a separate clear field?
And applying any Zero Knowledge schemes that checks:
1-all values in range to avoid overflow ( like explained in the paper)
2- (Sum of inputs-Sum of outputs)= the clear flag value which will be considered constant to the Zero Knowledge scheme
 
Is it simply due to lack of interest?
I mean all of that was back in 2018, but maybe now no one really demanding confidential TXs in Bitcoin, or what?