Why do they want me to stop breastfeeding?

My daughter is two months old. My mom calls me every night suggesting formula. My husband and I were both formula babies. I’m not opposed to it. I’m just confused why people keep suggesting it. I ask my mom why, she says, “oh it’s just good to do.” I also get other people wondering when I’ll stop breastfeeding. Has anyone else experienced this? What’s the reason?

Edit: My mom lives across the country. My supply is just fine and the baby has just turned 2 months and has gained 5lbs. She doesn’t have a weight gain issue. That’s why I’m so confused!