She's learned from experience that having something to bite down on helps when the fat cockhead and the first few inches of Tyrone's cock force its way inside of her sissy pussy.
Sure - for her it isn't quite the same as being filled with a huge cock. But when her sissy cuck is cleaning her lover's cum from her pussy, and bringing her to orgasm to boot, the pleasure she experiences is something her sissy can be proud of.
The expression on your wife's face when she's being filled with a huge cock is a thing of wonder for a sissy cuck to behold. How can a sissy deny his wife such exquisite pleasure?