It would be understandable (to me at least) if the first 10 or so did, as they would most likely already be pretty well off. But it seems very unlikely there was no one in that group of 56 people that wanted the money and prestige bad enough to convert. Was religion really THAT important back then?
The source I got of this is from this wikipedia page http://en.wikipedia.org/wiki/George_I_of_Great_Britain#Accession_in_Great_Britain which only states that: "The likelihood of any of them converting to Protestantism for the sake of the succession was remote; some had already refused.", which itself is sourced from the historian Ragnhild Hatton.
The stance of the Catholic Church was that if you are not Catholic, you are going to Hell. Even worse if you were once Catholic and then became apostate. An eternity of torment would not have been worth a kingdom to more religiously minded folk.
Additionally, if one were executed or tormented for ones faith in the Catholic church, that's pretty much a direct line to beatification and possibly even sainthood.
The Act of Settlement 1701 had made Sophia, Electress of Hanover Anne's heir (George was her son, she had died 2 months before Anne), so it wasn't merely conversion necessary to get back in the line of succession. Contesting the crown also would have required significant support from the English nobility which was unlikely to be achieved by what would be perceived as a conversion of convenience.
"Was religion really THAT important back then"
Yes and no. Monarchs would convert to gain power (Henri IV of France converted to Catholicism to be crowned and accepted by the Pope) and on that level it is not beyond the realm of possibility that one of the 56 would convert.
You always have to remember though, the king of England was the head of the church of England. Parliament, who were in a partnership of power in government, would never have allowed an ex-Catholic to rule the church - the Civil War was fought because Parliament thought that Charles' religious policy was too 'Popish' and James II was kicked off the throne for being a Catholic.
So religion was important to the common people and the nobles - it was the way they kept order and was a the glue that held communities of believers together; kings could and did change their religion, but it was more complex than that - they also had to be accepted by the powerful and wealthy in the kingdom.