Problem is, the whole site is database driven, and so adding more news items to the main page means that each one is an extra call to the database multiplied by the number of people visiting. We already have a lot of "too many connections" errors, and this would make the problem even worse.
Of course, if any tech gurus know more about the subject than I, feel free to chime in!
[PS - I'll slide this one over to Meta).