Why did most Christians stop observing their holy (Sabbath) day from sundown one day to sundown of the next day?

To be specific, "The Sabbath" is from sundown Friday to Sundown Saturday...While I can't point to a specific textual reference other than the Christian shift from celebrating the Sabbath(Saturday) to Celebrating "The Lords Day"(Sunday), "The Lords Day" is a celebration of the resurrection (Jesus died Friday and rose Sunday). With the shift to Sunday there was a setting aside of Jewish traditions and laws. The Jews follow the old Mosaic covenant, while Christians follow the new covenant (See Hebrews 8:1-13).

13 By calling this covenant "new," he has made the first one obsolete; and what is obsolete and outdated will soon disappear.

https://www.str.org/w/why-did-the-early-christians-switch-from-sabbath-to-the-lord-s-day-

https://www.catholic.com/magazine/print-edition/from-sabbath-to-sunday

"Nine of the Ten Commandments from Exodus 20:1-17 are repeated in the New Testament in one way or another. The only one not repeated in the New Testament is the fourth, the one about Sabbath-keeping."
https://www.gotquestions.org/Ten-Commandments-New-Testament.html