It's not difficult if yu "really" think about it.
The late 60's / early 70's rock fan was treated to the masculine figures of Daltrey, Jagger, Plant and Rodgers as stereotypes of the a-typical rock front-man. All of a sudden, the world would have had thrust into it's provincial working-class venues, a man of clearly questionable sexuality and a band with a highly quetionable name.
Rock pubs / clubs and their audiences simply were not prepared (or open-minded) enough to cope with Freddie and Queen. Hence, the band played to student audiences that were still heady with thoughts of sexual liberation and equality. Therefore, Queen played to Imperial College audiences (people that they knew primarily as friends anyhow) and other University bookings.
Britain at that time was an extremely homophobic place to live in.