Why grandparents have the tendency of overstepping their boundaries?

I’m currently staying with my parents and my two year old son. My son and I have a night time routine. As we were in bed getting comfortable to end the night. My son was fighting his sleep. So he got fussy. My mom came out her room into my room and says “Come on (Sons name) come and go to sleep with me.” He got up and followed her in the to her room because that’s what toddlers do. If you ask them to do something in a gentle voice they’re gonna do it. I went back to her room and got him because I wanted my son in proximity with me while we slept. Which I have a right to because he’s my son. After going to get him he was more agitated than before because he was now confused because of her prompting him to sleep in her bed for the night and he was still fighting his sleep even as I rocked him and talked to him but I knew eventually he would calm down but my mom wanted to keep coming in the room. She knows if he sees anyone come in the room during the night time when he’s suppose to be going to sleep he’s gonna cry because he then believes it isn’t bed time anymore. So, I set a boundary by simply telling my mom that she needed to stop coming in the room and that I had it. She then tells me “You’re waking up the house by letting him fuss. You aggravate him. He only does this with you.” And it hurt my feelings but it wasn’t true. She was only saying that because she couldn’t control the situation and I simply told her that he isn’t her child and that she can’t control everything. She just kept repeating that I aggravate him. Meanwhile he was calming down and finally dozing off. I’m currently in the process of moving out but it’s becoming a bit much living amongst her and my son in the same space. I need my own space with my son without any interference and the process of me moving out couldn’t happen sooner. I know she’s not doing it with evil intentions but she refuses to listen to me and not overstep.

Why grandparents have the tendency of overstepping their boundaries?
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