A great many people called for a boycott of Musharraf’s Pakistan when he seized power in 1999, though these calls became increasingly muted when it became clear that he didn’t fit the standard military dictator stereotype, and disappeared altogether after 11 September, when he became an important ally in terms of cracking down on Islamic fundamentalists.

Given that a potential (if not likely) outcome of a boycott might be to put them in power, it seems pretty clear why it’s not an especially popular cause right now – especially given that Pakistan, unlike Zimbabwe, has nukes.

Consistency would seem to demand action in both cases

Only if both cases were so similar that such consistency would be expected – and I’d argue that they’re not.