Partly because the chances of having T1 are very slim compared to having T2.
If you go to your GP with whatever complaint, they're looking at the most likely causes first, and move on the the rarer conditions if it turns out it's not the most likely cause.
Interesting @Antje77 know I really had to push - and my GP didn’t know how to order the tests, or how to interpret the results, but I just had this funny feeling - and I was right, it did come back as T1. My poor GP didn’t know quite what to say, bless him