#and the allegation about William coveting the earldom of Chester are implausible to me

[blackboar]

Why did William Stanley betray henry vii?

Sorry to be late. It's a good question, but my first answer got erased, and I ragequit for a time. First, I must point out that there still is controversy regarding whether Sir William Stanley did betray Henry VII. Evidence is slim, and we do not know the exact plan he had in mind, only 'treasonous' talk. I think he did attempt to support Perkin Warbeck and that there was a Household plot, or at least something resembling that, burgeoning at the Tudor court. Sir William Stanley attempted to revolt against Henry VII because I think he simply thought Perkin Warbeck was Richard of Shrewsbury. This is why he rebelled against Richard III. Recall Sir William was a servant of Edward V and consistently followed the House of York during its struggles against the Lancastrians.

When the House split in 1483, he remained loyal to Edward IV's progeny. Hence, his support to Henry VII which was support to his late master's daughter. Perkin Warbeck was another struggle for him because if he was Richard of Shrewsbury, then he was probably the rightful king in William's mind. William was sixty years old by then and a very dangerous foe to have, with the income of an earl and large cash reserves. His defection was a blow to Henry VII who managed to preemptively arrest him. Still, the 'betrayal' of William Stanley was a sign of enduring frailty for the Tudor regime.