I think if Karl V (who she wanted to wed) or Felipe II (who Karl offered) is off the market, Karl might push the Ferdinands as the only available marriage-age men in the family (Karl of Steyr is there, but he's a smidge young).
ICR where I read it but the main reason Maria refused (apparently) was because it would curtail her freedom or somesuch. Henry's death had little to do with it, since the proposal was made twice - once in the mid-1540s when Maria Manuela died (Karl turned his attention to the French girls
@isabella mentioned, but also to Lady Elizabeth Tudor and Archduchess Margarethe of Austria (daughter of Ferdinand I)), and again in the 1550s (after all those matches had fallen through the carpet) before Felipe II remarried (which is when Mary Tudor became the most eligible bachelorette in Christendom, and it
's probably then that wiki means). Unless I/the author misunderstood and there was only
one proposal.