I think you're failing to appreciate the full range of parenting approaches, and different children personalities in this.
For the most part, I think you're right. The vast majority of three year olds can cope with their mother going out to the evening.
I have two children with separation issues. The youngest was a bottle refuser with weight gain difficulties. Covid, when she reached about a year, so I might otherwise have tried going out in the evening, pushed that back to nearly two. Despite a very involved and loving father, frequently trying, she'd freak out if I wasn't there. Then she got ill and nearly died, I was always by her side. She's okay with me going out now, she's five, but she still finds it hard.
Her older sibling has had separations issues from birth. At a year old, If doing a protracted bedtime I'd pop to the loo, she'd panic to the extent of retching or vomiting. She got better but the impact of a poorly sibling set her back. She's fine with me going out, but if daddy does, I have to restrain her. About a year ago he stayed at a friend's house. My daughter literally sobbed all night. I got 20 minutes sleep. She was six at the time. Yes, we've been getting professional help, yes, we tried building it up slowly, It's better than it was, But it's still hard.
Our situation isn't typical. But I'm not sure any situation is. Everyone has their secret battles, and whilst many 3-year-olds go to bed independently and sleep all the way through, many don't. We don't know the reasons why these mums won't or can't go out at night. Most people don't know about our sleep/ separation battles, and I don't know about other people's challenges. Some women are just too tired, too much juggling of kids and work while still getting broken sleep. Will have lost confidence going out in the evening because kids and covid meant they didn't do it for years.
Practically speaking, suggest going around with a takeaway. I'd have loved that. Or going round during the day instead.