The collagen production in arterial walls is actually a normal, beneficial healing response – the problem is when it becomes excessive and chronic due to ongoing inflammation from insulin resistance.
Normal collagen in arteries:

Arteries naturally contain collagen for structural strength
Some collagen is essential and beneficial
It works in balance with elastin (collagen = strength, elastin = flexibility)

What happens in insulin resistance:

Chronic inflammation triggers ongoing collagen production
The body keeps depositing more and more collagen as part of its healing response to persistent vascular injury
The ratio shifts – too much collagen relative to elastin
This tips from beneficial (normal repair) to pathological (excessive fibrosis/stiffening)

The key word you caught: “EXCESS”
It’s not that collagen in arteries is inherently bad – it’s that chronic excess due to unresolved inflammation shifts the balance. Think of it like this:

Acute injury: Body deposits collagen to repair → heals → stops → beneficial
Chronic inflammation (IR): Body keeps depositing collagen because inflammation never resolves → excessive accumulation → arteries become too stiff → pathological

So, the body is doing what it’s “designed” to do (repair/strengthen damaged tissue), but when the trigger (inflammation from IR) never stops, the repair response becomes maladaptive.