Iracing Road cars vs formula cars

Hi everyone i wanted to talk about something that i've always asked myself but never got a response: why am i much more faster in formula cars than road Cars(especially GT3)? I play iracing since 2 years now and since the beginning i noticed that i felt more natural with formula cars compared to the gt. At first I thought that It was only a matter of time and practice that would have led me to the same "comfort" i had with formulas. However now after two years i improved a lot more in formulas and can constantly fight for top 5 in top splits but when i hop in gt3s( and focus for some serious time) i can't reach the same level.