There can be quite a few factors around school trips- for example:
-If a lot of students get busses in to school, then getting back for the busses has to be a consideration, and this can make trips very limited/stressful.
-Cost, as others have said, if schools can't afford to subsidise the trip, they need to know a minimum number of students will pay in order to make it viable. Schools get funding per pupil, it's not ring fenced for "trips" or "extra-curricular"- so your school may choose to spend their funding in a different way e.g. on nicer facilities or more resources in school. Or they may have higher running costs, etc.
-Staffing. Staff in state schools don't get paid extra to go on trips, even if they are very late back or staying overnight. In some schools you get a staff culture where people want to go on trips and see them as an enjoyable/important thing. In others people see it as a massive imposition, and therefore it's very hard to run these trips!
Another point around staffing is that if staff are out of school all day on a trip, someone has to cover their classes. If the school is already short staffed, this can mean SLT are reluctant to authorise trips. You need a higher ratio of staff to students, as well- taking one year group on a trip will involve at least double or triple the number normally needed to supervise them in school.
And yes, organising a trip is a huge amount of work- especially from scratch!
I do think it's shame for your daughter. Are there any local groups (youth groups etc?) she can join which would give her the chance to go on trips with people her own age?