Do Americans prefer to pronounce the i-sound as in: I my fly buy ...?

Because dialects differ. Obsolete roots are irrelevant for present-day language usage, that's like asking why Spanish speakers don't pronounce their Spanish like Latin--it's because they're speaking goddamn Spanish, not Latin. Languages change, including the pronunciations of loanwords, and including the pronunciations of loanwords that didn't even enter English through Latin. One could also go on a tirade about how Latin speakers didn't pronounce their words like speakers of Latin-Faliscan, but that would just make one a pedantic douche, now, wouldn't it?