I think you'll be enlightened by my previous responses on the Romanovs: on the laws of succession and on Alexei's illness. Basically, it didn't matter whether they had another son, because the problem wasn't "if they don't have a son/if the tsarevitch dies, there is no heir to the Russian throne" (one of Nikolai's male relatives would have inherited), but that, logical or not, having several daughters and then a sickly son seemed like divine statements on their right to rule.

But also, as I've noted in earlier answers, Alexandra was chronically ill and in pain. This isn't often discussed, probably because it gets written off as the fancies of a lazy woman, but it would certainly help to explain why the couple would stop once they had a son.

Hey there,

Just to let you know, your question is fine, and we're letting it stand. However, you should be aware that questions framed as 'Why didn't X do Y' relatively often don't get an answer that meets our standards (in our experience as moderators). There are a few reasons for this. Firstly, it often can be difficult to prove the counterfactual: historians know much more about what happened than what might have happened. Secondly, 'why didn't X do Y' questions are sometimes phrased in an ahistorical way. It's worth remembering that people in the past couldn't see into the future, and they generally didn't have all the information we now have about their situations; things that look obvious now didn't necessarily look that way at the time.

If you end up not getting a response after a day or two, consider asking a new question focusing instead on why what happened did happen (rather than why what didn't happen didn't happen) - this kind of question is more likely to get a response in our experience. Hope this helps!