Your observations are quite correct. According to a recent study of 122,385 Medicare patients, white men are more likely to have both knees replaced at the same time. And white men in a higher income bracket are more likely to do so compared to white men with a lower income.
It's not clear if this is a case of gender bias or simply a matter of who has a caretaker at home to help out after surgery. Since people over age 65 are the most likely candidates for TKRs, and the culture is one of women as caretakers, the greater number of males having both done at the same time may not be too surprising.
It's possible too that more women intend to have the second knee replaced but complications occur. Or once they have the first knee replaced, their function is so much better, they decide to get along without having the second one replaced.
Without specific studies to answer this particular question, it's merely speculation at this point. Large studies such as this one can review the records but don't interview the patients as to their intentions and factors in decision-making.