Do you know the reasons behind Muslim league success in 45-46 election? If yes then it so easy and simple, to know the reasons of defeat, just reverse the reasons of success and you'll get the reasons of defeat. Let see in next lines.

Although I have not read this, but just analysing and seeing the situations of those years I can give you some hints, and you may further explore those.

As you know Quaid e Azam Muhammad Ali Jinaah was In The Britain (had left his politics in Subcontinent owing to his disappointment over the behaviour, mis-trust, self interests of other Muslim leaders. So you get two points from this.
1 All the Muslims leaders had their own interests and there was disintegration in Muslim league. This obviously was main reason

2 The only real leader of Muslims was away. So this was also an other reason.

Among Muslim leaders present in India, Allama Iqbal was ill and in his last days of life (He fell ill in 1933), Don't know the exact year when he resigned Presidency of Muslim league.

I am also not sure which leaders among Ali brothers and others were present at that time or not, and what was their condition. So in short lack of leadership was the main reason.

An other important point was the aim of Muslim league which in contrast to 45-46 elections was purely absent (it was not for a separate country) There were no popular slogans.

An other reason was less financial resources of Muslim league as compared to The Muslim leaders of Congress which were competing Muslims league leaders. And hence The Muslim leaders of congress could easily win, because of financial resources.

Now if you reverse these reasons you'll get the reasons behind Muslim league success in 45-46 elections.

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"The only necessary thing for the triumph of evil is for good men to do nothing."
--Edmund Burke (1729-1797)