People generally don't say "He is taller than I" because they have poor grammar.

"He is taller than me" grammatically makes no sense - but people use it all the time. In fact they use it more than the correct construction.

The reason you use "I," as you do in most languages, is because the sentence is really "He is taller than I am." Often times it is shortened to "He is taller than I" - and for some reason people aren't used to saying that.

In general, most people don't end a sentence with "I" or even use it unless it is the subject of the sentence.

Good rule is to just complete the sentence. People will incorrectly but often say"He is a better singer than me" when they should say "he is a better singer than I." You are always safe to just say "he is a better singer than I am."

Oh, something funny. I was watching TV and this dumb person said, "My sister and me went...oh, I mean: I and my sister went..." I guess the latter is a bit closer...