Why was I declined a higher credit line on my Visa?

My credit score 747. My school loans, car loans, dept cards, etc are all paid off. I have one open credit card maxed to 9000 on Citi mastercard. My Visa is up to 3400, I asked for 4000 more credit line. Why was I declined? They told me some bs because I was too high on my CitiMc. I don't believe this. Anyone else go through the same thing?