Well, there had been multiple people escaping the camps and reaching the Allies to tell them what was going on. And they knew a lot about it while it was undergoing. They even broadcasted a condemnation of it in 1942.

But when it comes to their war goals, those weren't about the holocaust. Germany and Japan both were aggressors who threatened to conquer large parts of the world and both regimes killed millions of people. And both were at war with the US and the UK, so beating them back until they couldn't be a threat anymore was the main objective.

In fact, often by not targeting the railroads to the death camps and by sending Jewish refugees back to their deaths the Allies showed their overall indifference at worst and ignorance at best of the genocide going on.

Well, you have to try to look at it from their perspective. We know that Germany would lose the war in 1945 and that by 1943 the war was pretty pointless from a German and Japanese perspective. Both regimes however fought on and the resistance of both respective countries stiffened the closer defeat came. Germany lost more soldiers during the last few months of the war than during the entirety of the first years. For the Allies that meant that they had to chose between crippling the German war machine or allocate their bombers, which had horrific casualties, to targets without that much military worth while they also were further away from Britain/Italy than German industrial centers. So to them, with their main goal of defeating Germany, it made sense to focus on crushing the military power and end the war asap.

In regards to them sending back refugees, well, I guess that is why they also didn't talk about it too much overall. It would've been quite a bit of shame for the countries to have to acknowledge that they sent thousands of people into their certain deaths. As pointed out in one of the articles I linked, especially during the Cold War they tried to swipe it under the rug as much as possible. Now, with the Cold War over and the generation of WW2 mostly gone, we see Canada's prime minister openly speaking about the shame.

I would definitely agree with your characterisation in the second question e.g. that the ending of the holocaust was a byproduct of the Allies' true goal: winning the war.

The way that we remember WWII today is not at all how those who lived through it would have remembered it, in the years and decades following. The prominence of the Holocaust in popular memory of WWII is actually a fairly recent phenomenon. It's really not until the late 1970s that the Holocaust becomes a part of popular memory of WWII. The term "Holocaust" is coined around this time, weirdly enough by an American mini-series starring Meryl Streep released in 1978, called Holocaust. Before this, it was simply known as the Nazi atrocities and/ or the Nazi genocide. Thus, the vision that we have now of WWII, being a war against Nazi atrocities, is certainly misplaced. We also have to remember that for example, the Holocaust was only incidentally mentioned in the Nuremberg Trials, it was not a primary focus even though most people today think of the Nuremberg Trials as being the trials for the Holocaust.

Another feature which is distinctly absent from present day popular memory of WWII is the level of racism generally, and anti-semitism specifically that was prevalent within the Allied nations themselves. Many countries for example, continued to have their own eugenics movements, similar to the Nazi eugenics movement in their concerns about 'racial hygiene'. Karl Pearson, father of modern statistical methods and first holder of the Galton Chair of Eugenics at UCL was, as late as 1925, still researching the negative impacts of Jewish migration on British racial stock. Similarly, in 1932 British MP Oswald Mosley start the British Union of Fascists, which, while ultimately outlawed once the war breaks out on suspicion of supporting Axis powers, had an anti-semitic, anti-immigrant message which resonated with significant portions of the British electorate.

So yeah, there is definitely room to argue that there is some pot, kettle, black nonsense going on in popular memory of WWII.

However, with regards to your first question, if we want to assess the level of "moral credit" so to speak that given societies get for their history we must also consider the historical context in which they were acting. Were Allied powers also racist and anti-semitic? Hell yes! Did they de-prioritise ending the genocide in order to win the war? Arguably so. Does that mean they should get no moral credit? Debatable. The world in the 1940s was an incredibly racist place by today's standards. And even though Allied powers often exhibited traits which they would later condemn the Nazis for, they did so to a visibly lesser degree. In sum, a more accurate perception of the Allied role in the Holocaust is somewhere between noble liberator and callous enabler.