Children between 2 and 12 can sit still for hours if you train them to, Salem. Not stock still, but they can sit quietly even with a certain amount of wriggling, turning around, alternating being held and sitting on a pew, and they can watch what's going on. They do it every Sunday at the church I attend.
They have zero interest, they can't play, they can't run around...
It's important to condition children to understand that they are not always going to be able to play or run around and that not every event is going to be set up for running, climbing, or noise.
This is achieved by having times at home where they need to observe a certain amount of decorum - having to sit for meals, for instance, and not leave their seat or leave the table until the food is finished and they ask to be excused - and by bringing them places where they can't do this, prepping them beforehand, maybe bringing some quiet distraction like crayons and paper or a quiet non sugary snack to pick at, and praising them as they go along for the behaviour you want to see. It would be asking for trouble to bring a child to an occasion like a wedding for their first solemn outing, but they could be brought to less high stakes events on a consistent basis beforehand, like the odd church service or storytime in the library, to get some practice in.
Children older than about four should have some interest, or enough experience being bored that they don't consider it a problem that the parent needs to fix. You can make it interesting for them by pointing out things you have talked about or read about beforehand when they happen.
The assumption that children are only interested in a limited menu of events and that they need to be provided with certain sorts of entertainment or they will be bored is strange. YYY to LoniceraJaponica's comment Children aren't allowed to be bored these days. It is not a problem that a child is bored unless the parents have considered it a problem and have always taken steps to fix it.
What's in it for them? Approval and appreciation from parents.
If I had a child older than 4 who couldn't manage ninety minutes of quiet or show some interest in what was going on I would wonder what had gone wrong.