I always interpreted "Pon Farr" as basically the equivalent of (forgive the lewdness) being horny. It's crude, but that is essentially what it is.
The Vulcans, as a race which suppressed emotions, may also have suppressed their sexual behaviour, viewing it as uncivilised and limiting it to every 7 years, the maximum time they can realistically delay sexual activity until their biological imperative takes over. This is why they lose their emotional control during Pon Farr and behave erratically.
Romulans have not suppressed their emotions, therefore they have the drive to have sex and procreate, but like humans, do not place any limitations on it, therefore they do not go through Pon Farr because the pent up sexual tension that is Pon Farr only occurs when you deny yourself the pleasures of sex.
If humans developed a purely logical society and eschewed sex, we too would have a biological imperative to have sex, and would probably develop ritual around how this imperative is allowed to be expressed.