Judging by the reaction in this thread, I can't imagine what the responses would be in an atl in which Hitler died or got overthrown prior to 1939 and someone started a thread saying "WI Hitler lives, negotiates economic cooperation and near-alliance with USSR?"
Germany at least had pre-existing military and economic ties to the Soviet Union.
Was there any particular reason for this?
After WW1 and the success of the Bolshevik revolution in Russia, Socialist parties across the world faced a civil war between those who thought it best to emulate the Bolsheviks and those who remained committed to pursuing socialist goals by democratic means. This left the vast majority of Social Democrats deeply bitter since the struggle in most cases undid decades of work.
Further, between WW1 and WW2, Moscow constantly interfered with leftist parties, usually to the detriment of Socialism in whatever country concerned in their quest to obtain advantage for the USSR. This created plenty of bitter former idealists who'd seen their parties used and discarded by Lenin and Stalin.
And then, people of leftist politics were more likely to travel to the Soviet Union and see it for themselves. Some of those, of course, liked what they saw, but plenty came away ardent anti-Soviets. Some also never came back at all. Yet another name in the long list of victims murdered by the Soviet regime (Stalin absolutely gutted the leadership of foreign socialist movements during his purges - if a less murderous regime had been in charge history - particularly in the 3rd world, would have been very different).
Add to that, most socialists also tended to care for the interests of their nation and most nations were not so positioned that they would profit from taking the Soviet side when most of the world's trade moved across oceans that were controlled by the US navy.
For Britain that last point is particularly salient, since Britain was an island nation whose day could be decisively ruined by the USN and for whom trade with the US itself was particularly large. As such, even if Attlee were for some reason to become very pro-Soviet, it is hard to see him following a policy which was strongly pro-Soviet unless this is also a world in which the US is for some reason isolationist.
fasquardon