I can think of two very good reasons for not splitting an infinitive.
1. Because you feel that the rules of English ought to conform to the grammatical precepts of a language (Latin) that died a thousand years ago.
2. Because you wish to cling to a pointless affectation of usage that is without the support of any recognized authority of the last 200 years, even at the cost of composing sentences that are ambiguous, inelegant, and patently contorted.
And it’s not just split infinitives. A lot of our grammatical rules are baseless or even dumb.
There are no officially appointed guardians for the English language, so who sets down all the rules? The answer, surprisingly often, is that no one does, that when you look into the background of these “rules” there is often very little basis for them.
English grammar is so complex and confusing for the one very simple reason that its rules and terminology are based on Latin—a language with which it has precious little in common. Making English grammar conform to Latin rules is like asking people to play baseball using the rules of football. It’s a patent absurdity. But once these insane notions became established grammarians found themselves having to draw up ever more complicated and circular arguments to accommodate the inconsistencies. One authority, F. Th. Visser, found it necessary to devote 200 pages to discussing just one aspect of the present participle. That is as crazy as it is amusing.
I can tell you why I am (sometimes) a grammar snob: Pride. I feel like I’m part of an elite club who knows when and how to use “whom” correctly, for example. “Whom” has a thick whiff of pretentiousness, and yet I use it because it makes me feel smarter than 72% of the population.
On the other hand, there are other grammatical rules that I ignore just because I feel like it. Using “one another” for more than two people instead of “each other,” I just won’t (usually) do it, because “one another” feels way too polite and British.
Then there are other grammatical rules that I despise, like not using a word that isn’t in the dictionary, or using a word in a way it wasn’t intended (e.g. using a noun as a verb or an adjective as a noun). To me those violations are the most exciting part of language, and any grammar snob who says differently will get smacked if they come within my striking range.
