Our local surgery advise people with chronic conditions to get the flu jab.
With diabetes I would imagine it's the blood sugar level going out of control with all of the dangers that incurs.
Speaking for myself, I have MS, flu is very likely to trigger a relapse. If this happens, I lose the ability to use certain parts of my body. This may improve when the flu passes, it may not. I would prefer not to take the chance. Who needs the use of their legs anyway.......
OK - CLKD you may be fine with getting flu, but it gets passed around, others are affected, it's not just you.