Because it's not all that great. It's the C Programming Language of linguistic style guides—well-respected and historically relevant, but not necessarily the best resource.
For example, The Elements of Style tells you to avoid the passive voice, on the grounds that sentences like "The sandwich was eaten by me," are much more awkward than "I ate the sandwich." It gives three sentences in support of this: "There were a great number of dead leaves lying on the ground," "It was not long before she was very sorry that she had said what she had," and "The reason that he left college was that his health became impaired." None of these sentences actually contain a passive: the first is an existential sentence, the second is a simple copula, and the third uses the copula with an adjective, not a participle.[1]
All of which is to say—Strunk and White did not know what a passive was. The actual advice they meant to give is something along the lines of, "Don't be vague about agency," but that is a different proscription. There are places where you should avoid the passive, and there are also places where you should employ the passive, because it is clearer than the alternative. For example, if your documentation says, "Our software product is used to [blah]", you should not change it to, "People use our software product to [blah]," because those people do not matter. By avoiding the passive, you have made your writing less clear by introducing unnecessary information.
Strunk and White have a lot of advice which is merely harmless, but it is not a spectacular writing guide, except for the simplest, least elaborate kinds of writing. Truly great writing is not writing which follows those rules, but writing that knows when to follow such rules. For example, Orwell and Churchill, both quite excellent writers, use the passive significantly more than journalists of the time[2].
[1]: The passive transforms sentences of the form "{noun1} {verb} {noun2}" into "{noun2} {be} {verb}ed [by {noun1}]"; it is (or should be) clear that these sentences cannot be transformed from the latter pattern into the former.
Isn't the usual advice to keep software as the subject of the sentence but rewrite the verb? Like: "Our software manages your source code revisions" rather than "Our software is used to manage source code revisions?".
(I totally agree that the "no passive voice" rule is oversubscribed btw.)
I usually come across people who don't actually know what a passive is[1] or who are completely and rabidly anti-passive, but I don't doubt that such advice is common among more reasonable grammarians. Still, there are sentences that are difficult if not impossible to rewrite in such a way because of context or lack of vocabulary, e.g. "... and the network interface is written in C," is difficult to rewrite because the old information (the software) comes first, the new information comes at the end, the unnecessary agent is omitted, and no active verbs come to mind.
For example, The Elements of Style tells you to avoid the passive voice, on the grounds that sentences like "The sandwich was eaten by me," are much more awkward than "I ate the sandwich." It gives three sentences in support of this: "There were a great number of dead leaves lying on the ground," "It was not long before she was very sorry that she had said what she had," and "The reason that he left college was that his health became impaired." None of these sentences actually contain a passive: the first is an existential sentence, the second is a simple copula, and the third uses the copula with an adjective, not a participle.[1]
All of which is to say—Strunk and White did not know what a passive was. The actual advice they meant to give is something along the lines of, "Don't be vague about agency," but that is a different proscription. There are places where you should avoid the passive, and there are also places where you should employ the passive, because it is clearer than the alternative. For example, if your documentation says, "Our software product is used to [blah]", you should not change it to, "People use our software product to [blah]," because those people do not matter. By avoiding the passive, you have made your writing less clear by introducing unnecessary information.
Strunk and White have a lot of advice which is merely harmless, but it is not a spectacular writing guide, except for the simplest, least elaborate kinds of writing. Truly great writing is not writing which follows those rules, but writing that knows when to follow such rules. For example, Orwell and Churchill, both quite excellent writers, use the passive significantly more than journalists of the time[2].
[1]: The passive transforms sentences of the form "{noun1} {verb} {noun2}" into "{noun2} {be} {verb}ed [by {noun1}]"; it is (or should be) clear that these sentences cannot be transformed from the latter pattern into the former.
[2]: http://itre.cis.upenn.edu/~myl/languagelog/archives/003414.h...