Why do SDA’s teach that “the Covenant from Sinai” is still in force?
A covenant is merely an agreement and the agreement is what was faulty (i.e. "God found fault with the people . . . because they did not remain faithful to [His] covenant"). It should be obvious to any unbiased person that a perfect God didn't find fault with His perfect law (i.e. what was covenanted/agreed upon by both parties should be observed.). Interlopers who self identify as something they're not promote false teaching to, if possible, deceive the elect.
Speaking of the Ten Commandments Paul refers to them in the present tense calling them "holy, righteous and good." So it is apparent that the covenant/agreement came to an end, not what was agreed upon.
I pray this helps.
But for the grace of God go I,cyspark