For one thing, later confessions/creeds will often aim at showing their consistency and conformity with the faith as expressed in the past. "This we STILL believe."
What this church body or that chooses as it's "doctrinal standard" is that form-of-words which expresses what (in Protestant circles) they believe summarizes faithfully biblical teaching. These are the things they say with
one "heart and mouth." A confession is a "saying-with" (as a "profession" is a (saying-forth"). The agreed-upon statement then forms a basis for regarding some party as teaching properly a certain doctrine.
Previous confessions are valuable as historical markers, as a record of the church's witness tying the present to the past. One can also study them to see if some present statement is contradicted by some past statement; either to justify the past or the present when compared to the Bible (as the unnormed-norm, or the norming-norm).
The Scots Confession was superseded in the mid-17th century, when there was a fresh effort (begun in Cromwellian England) to unite the church in these kingdoms under a single Reformation statement of faith. The finished product (the Westminster Standards) was never adopted by the Anglicans; while the Scots adopted it in anticipation of union that never took place.
The integrated and very thorough Standards (Confession and Catechisms) were kept by Presbyterians, and the Scots Confession became an historical artifact.
It was laudable for churches all over in the days of the Reformation (be it in the Lowlands of the continent, the mountains of Switzerland, the Isles, etc.) to draft statements of their own, perhaps patterned on other places' statements, to be the vernacular confession of yet another place. There are multi-volume collections of Reformed confessions from all over Europe you can buy today, for example:
https://www.amazon.com/Reformed-Con...rd_wg=PgsXZ&psc=1&refRID=F1VS6P4G51J522XP66C1
The key to appreciating what is collected is noting the consistency in the Faith confessed, across nationalities and languages (these are translated). What all or most have
in common, is self-evidently the core of what the Reformed confess.