Originally Posted by The Judge
If you're narrating in present, ie what's happening today, and you want to say it's as a result of something that happened yesterday, you have to go into past tense to do it, (ie "Yesterday we sold the horse, that's why I'm walking") unless you're striving for a "Well, I says to him" or a Damon Runyon effect.
But Damon Runyan is not, sad to say, alone. If the narrator is a UK historian (at least, one of those who appears on Radio Four), there's a good chance that they'll use the present tense for everything and anything in the past.
I assume they do this to give greater immediacy to the past - or to "make it relevant"? - but all it is is very irritating.