What's the rationale behind some families sending their son to more expensive schools than their daughter?

My BIL has two kids, daughter (8F) and son (5M). When their daughter was younger, she wasn’t sent to a playschool and was directly admitted to a mid-tier school in the city with an annual fee of around ₹30K. However, their son was sent to a playschool at 2-2.5 years old, where the annual fee was ₹60K. Now that their son has completed playschool, they are enrolling him in one of the most expensive schools in the city, which costs around ₹2L per year. This school has small class sizes (around 30 students per class) and a strong emphasis on extracurricular activities. Meanwhile, their daughter will continue in the same mid-tier school, which primarily focuses on academics with little to no extracurricular opportunities. With around 65 students per class, the teachers understandably struggle to give individual attention to each child . They believe that if their daughter studies in an expensive school, she will develop "high expensive demands" by being around wealthier kids. They also claim that students in such schools focus less on academics and even 10 YO kids get into relationships. They also say that they can’t afford to send both kids to the expensive school. But here’s what I don’t understand If being around rich kids leads to "increased demands" and less academic focus, wouldn’t the same apply to their son? In today’s world, where both boys and girls need education and need to become financially independent adults, how is this fair to not offer your girl child the same opportunity? I tried reasoning with them calmly, but they’re adamant about only sending their son to the expensive school. It just doesn’t sit right with me.