The quote "Credo quia absurdum" (I believe, because it is absurd) is ascribed to Tertullian. But Tertullian never wrote this: what he wrote (De Carne Christi, V, 4) was "Prorsus credibile est, quia ineptum est" (It is wholly believable, because it is incongruous). These two phrases, though somewhat close in meaning, are completely different in wording. So where did "Credo quia absurdum" really come from? Is it someone's deliberate paraphrase of Tertullian, or a misquotation, and if so whose? Who was the first to use it?
It looks like a paraphrase made by the Zen Buddhist D. T. Suzuki's book, "Introduction to Zen Buddhism". Although, D. T. did use a different phrase beforehand, and it's possible that the paraphrase came before this writing (which was in 1914). The line quoted by Suzuki comes one line after the original line in question in Tertullian's work, so they are quite closely related. As Suzuki suggests, this phrasing may make more logical sense. It also is shorter, and thus lends itself to brevity.
I am not a Latin Scholar, but I had three courses of Latin in High School in addition to extra-curricular Latin interests and exploration. I can say that, for the original quote, the repetitive usage of "est" (He/She/It is) is likely annoying and/or feels rather choppy to those who speak and read Latin fluently. Often times, the verbs of the form "to be" in Latin are implied, either by other verbs or simply by the mutual understanding that they are there (which can make it more difficult for those of us who don't read Latin on a regular basis to understand). I am unsure, but this could be (in written Latin) due to the fact that ancient man needed to use his paper-like resources carefully, since they did not have paper sold for less than a cent per page back then. It was a much scarcer resource.