It could be easier…
I see Revit behaving this way, they regard the first point as ineligible to being tangent because it depends on the bearing of the line, With that assumption or bias, the first point is necessary to make a tangent condition possible. I can easily snap to a location on the circle (a pulley for example) that couldn’t be tangent to the next pulley.
AutoCAD deals with this in a clever fashion (when we invoke the tangent snap) by fixing (changing) the first point to be tangent after the second point is placed. If we aren’t careful with our second pick point (snap tangent too) the tangent line might end up on the opposite side of the pulley.
In contrast, Revit handles it naively, because it regards our first point as ineligible to tangents because it isn’t considering the desired end…