I don't know why my top tier always tilts like this. I always use at least 8 fat plastic straw as dowels and a cake board under the top tier. Does anyone know how to fix this problem?? Thanks in advance for your replies!

There is no picture attached? Did you intend to post a pic, because nothing is showing?

Without seeing it I can only guess that somewhere your cakes are not level..you are maybe cutting the straws to the cake level instead of to each straws height?

Even a little variation in height will affect your cake.

I use a spirit level on my cakes to make sure they are perfectly flat before stacking.

Somewhere in your tiered cakes there is an imbalance...laws of physics lol x