I'm wondering why are my teeth so sensitive?

Other causes. Gum recession, exposed roots, gum line wear or decay all cause sensitivity. And tooth grinding can cause sensitivity as well.
Enamel deficiency. Teeth can be sensitive for a variety of reasons. Enamel is the hardest substance in your body, even harder than bone. Enamel protects your teeth & insulates them from thermal changes. Cavities, acidic drinks, gingival recession, etc. Can cause the loss of enamel resulting in sensitivity. Dentists can help figure out what specific factors contribute to your sensitivity & may help alleviate them.