“You can maintain proper hygiene even without intermingling.”
Last time I checked they had sinks and showers in the dormitory of boys yeshivos and girls seminaries. I am certain they are not used only by those who have a shidduch meeting later that evening. You know what they say, “like flies, if you ignore your teeth, they too go away”.
“then why is someone who previously neglectful of hygiene but then cleans up only doing it to ingratiate himself with the opposite gender?”
When I was in Yeshiva, those who neglected their hygiene were called “greasers”, which was evident by the slick atop their head and the shine on their face (and unfortunately, if you sat too close, evident on their breath). Those same bachurim were never seen on the bus at any time, they were always in the beis medrash. Its been a LONG time since I’ve used the bus on a regular basis, have things changed?