For the health of the mother it’s wise to space pregnancies apart, by 18 months according to the WHO. There’s increased risk for a lot of things for closely spaced pregnancies, so the condoms are a pretty good idea.

Perhaps for STDs, any infection is more difficult during pregnancy - and an active infection of the birth canal can also complicate delivery.

Because with modern nutrition a woman can get pregnant again very soon after giving birth. But that is not healthy for the woman or her babies.