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How is this relevant to the question on sola scriptura? You say "nowhere in the Bible does it explicitly state that this change took place" yet where in the Bible does it explictly state that the Bible is the sole source of all history and doctrine?

To your matter read Ignatius of Antioch, Barnabus and Justin Martyr who observed Sunday as the day of worship. And just after them, you have Dionysius, Clement of Alexandria and Tertullian

"[T]hose who were brought up in the ancient order of things [i.e. Jews] have come to the possession of a new hope, no longer observing the Sabbath, but living in the observance of the Lord’s day, on which also our life has sprung up again by him and by his death" (Letter to the Magnesians 8 [A.D. 110]).

Barnabas 74 AD. "Wherefore, also, we keep the eighth day with joyfulness, the day, also, on which Jesus rose again from the dead"

Justin Martyr 140 A..D. "Sunday is the day on which we all hold our common assembly, because it is the first day on which God, having wrought a change in the darkness, made the world; and Jesus Christ our savior , on the same day rose from the dead."

Didache 80-90 A.D. "And on the day of our lords resurrection, which is the Lord’s day meet more diligently."

Sabbath commemorates a finished creation with rest, the last day of the week. In contrast, Sunday is the dawn of the new day, of a new covenant.

Tertullian said of these practices that "without any written instrument, we maintain on the ground of tradition alone": Baptizing by immersion three times, giving the baptized a "drink of milk and honey," forbidding the baptized to take a bath for a week, kneeling in Sunday mass was forbidden, and the sign of the cross was to be made on the forehead. (De Corona 3-4)

Jerome said that these "observances of the Churches, which are due to tradition, have acquired the authority of the written law." (Dialogue Against the Luciferians 8)

Why aren't these traditions observed anymore?

“Sabbath commemorates a finished creation with rest, the last day of the week. In contrast, Sunday is the dawn of the new day, of a new covenant.”

Nowhere in the Bible does it teach this. Sure the disciples preached on the first day of the week (as well as the other days of the week) but if the first day (or eighth day if you prefer) were to be recognized as The New Day to worship from henceforth, it would have been proclaimed as clearly as the Sabbath one (Thou shalt . . . )
By the way why does the fourth commandment start with REMEMBER the the Sabbath as though mankind would forget?