In evolutionary terms, humans who want sex will procreate, leading to more humans who want sex. Desire for sex (in this case I'm talking about hetero piv sex) is built into our biological makeup. I grew up in Ireland where contraception was not widely available prior to the 1980s (due to the Catholic church despising women) and one older woman commented to me that in her time people used to get married just to have sex as having sex outside of marriage was too dangerous (given said woman hatred).
Pre contraception a desire for piv sex, barring any fertility issues, would eventually lead to children - you just accepted it. Many women ended up with far more children than they would ever have chosen to have. Now, with contraception, you can fulfil your desire for sex without a baby ever being a possibility, which turns having children from an inevitability into a choice.
On the whole, that's a good thing - my gran had nine c-sections and almost died on the last one, which is barbaric. However, from looking at my own friends, it seems like the freedom of choice has also added an element of paralysis, where people feel it's wrong or foolish to have children unless you can give them a certain standard of living. I know people who definitely have the desire to have children but who are incredibly hard on themselves in terms of their expectations - they feel they have to have a house of a certain size, a certain income etc before they can even consider having a child. Being a parent has turned into a normal life event open to all to something that is only accessible to certain people who meet certain criteria. It worries me because I feel some of those friends will miss the boat and have huge regrets.
I also wonder what impact hormonal contraception has on the desire to have babies (I've never taken hormonal contraception). There's no getting away from the fact that having a baby isn't really a rational decision, for women in particular. It's a massive and terrifying undertaking that is likely to have at least some negative impact. My wish to have my first child was definitely hormonal - I wasn't in a good place financially, DH and I were renting but I was fixated on having a baby. I just knew I had to have one. Would I have felt that way if my hormones were being controlled artificially? If I'd had to make the decision in a really rational way and come off the pill to make it happen, would it ever have happened? I feel like the hormonal desire pushed me towards the decision - without it I wonder if the practicalities would have seemed too overwhelming.
Perhaps women who are on the pill but who are undecided about babies should come off the pill for a while (use condoms or something else) and see how they feel then?