I think unless you desperately wanted a child, got to late 30s (or younger with known fertility issues) and hadn't met anyone despite trying to settle down you have no idea of what it feels like to make this choice that can be so hard if you really tried to find a partner or lost one whilst time ticks by.
It is so different from thinking about children vaguely but not wanting one, then only deciding to have a child when you meet your partner (in plenty of time). The urgency and panic feelings of time running out can be so awful. Like a feeling of 'can I get to the hospital before my loved one dies?!' intensity, but over years.
Plenty of people choose it first off too but that's for potentially different reasons. Think it's on the up?
I do think it is different to leaving/being left or single when pregnant because you are going into it eyes open, planned, knowing from ttc with donor not just from pregnancy at the end of the relationship etc, that no one will ever share your special parental moments, that you will be doing all the appts, feeds, experience the fears and pride without a partner.
Not saying any is better or worse, but different in my mind. Ramblings over. Hope that was helpful OP!