Why are my doctors scared about placental insuffincy if they haven't done a ultrasound to even see and im a type 1 diabetic (well controlled)?

Diabetes in pregnanc. I'm sure your doctors are not "scared" , maybe concerned would be more appropriate. Diabetes, as i'm sure you know, affects your blood vessels and therefore your circulation. The same goes for your placenta when pregnant, they're not as efficient as a non-diabetic's. That's why they're likely checking your baby's growth regularly, doing nst's, & recommending delivery no later than 38.5-39 weeks.
Preventative. Patients with diabetes have increased risks of having placental issues later in pregnacy. Not knowing how many weeks you are makes this hard to explain in more depth.