When do you use "this is because" in the present tense versus "this was because" in the past tense?

I found this from a blog where the writer used this is because:

Through the experience of the DSCE, I felt like my life goal had finally been achieved, but when I desperately pleaded with God to let me back into that state, I soon realized it was almost impossible to achieve on my own. This is because I had only become partially self-realized.

Shouldn't the author have used this was because because they were
referring a past event? If not, can someone please explain the rule
regarding when to use this is because versus when to use this was because?