Because it had not happened so his love had died.
Catharine felt this, and she died of it.

But not suddenly, not at once, did death release her from her sorrows and racking tortures.

Six months she had to suffer and struggle with them.

After six months she died.
Strange rumors were spread at her death; and John Heywood never passed by Earl Seymour without gazing at him with an angry look, and saying: "You have murdered the beautiful queen! Deny it, if you can!" Thomas Seymour laughed, and did not consider it worth his while to defend himself against the accusations of the fool.

He laughed, notwithstanding he had not yet put off the mourning he wore for Catharine.
In these mourning garments he ventured to approach the Princess Elizabeth, to swear to her his ardent love, and sue for her hand.