Because for 100,00o years that's how relationships worked. What society didn't have men marrying females as soon as females became developed?
You can't go back to the fucking 50s, 60s, and 70s and prosecute people for today's standards. Yeah, that's fine for today's 20-something who barely knows shit but the blame game and social media mob justice, but it doesn't work when you look at shit in context.
You know what was frowned upon in the past that isn't frowned upon today? Having children out-of-wedlock. Parents would rather their 15-year-old go get married than have a kid out-of-wedlock. Shit happened to my aunt. No one gave a fuck about 18,16 or whatever number decades ago. The residual effect of eras past is why R kelly got away with Alliyah. That was only 20 years removed from the 70s. Hell, we damn near 20 years away from 2000 to put that into context.
I'm not making excuses for these people. I'm saying times have fucking changed and the laws protecting females are a relatively recent invention of WESTERN society. And by recent, I'm talking post fucking 1960s. They Civil Rights type recent. And that's going against 10s of thousands of years of history that encompassed the entire globe, not just 400.