If any store used dynamic pricing to expand their margins, the others would just do the same and compete away those margins once again, with the marginal gain being handed back to consumers.
Dynamic pricing on personal data is bad I think, but temporal dynamic pricing is actually very good for everyone and I hope it doesn't get thrown out by some reckless legislation-writing.
How would you do it if pricing is dynamic and changes every day?
By the time competitor finds out about the price, you might have already reduced it, making it look like theirs is more expensive even after they applied discount.