私にそれがよく分かりません

In this sentence, 私 is said to be a dative subject and それ to be a nominative object. If they are named after their case markers, I wonder why we cannot simply regard に and が as a nominative marker and an accusative marker respectively? There seems no nominative-ness in それが to me, same thing for 私に.

愚問かもしれませんが、お教えください。

私にそれがよく分かりません

In this sentence, 私 is said to be a dative subject and それ to be a nominative object. If they are named after their case markers, I wonder why we cannot simply regard に and が as a nominative marker and an accusative marker respectively? There seems no nominative-ness in それが to me, same thing for 私に.