Why do you think it is usually so hard for people to change their opinions on something?

Wise words for so young a man.
But you must remember that what you call opinions also are our norms and basic values.
We are gregarious or social creatures and in order to fit in and function in our social group and community we need to share and be adjusted to the group's norms and values. If our opinions differ too much from the group's norms and values it causes conflicts. To many and perhaps most people being normal seems to be extremely important and few give it a thought that the normality is a matter of social norms that can differ very much depending on where in the world and under what circumstances you live.
Having the opinions, values and norms that identify us as members of the group we belong to can be a matter of survival and at least it is part of what decides if we are successful in life.

Because we already like our opinion. Sheesh

I think your observation is astute.