Vaccines

Hooray, New Zealand gets a measles outbreak. Whether it's due to middle-class antivaxxers, or kids whose parents just have a hard time getting them to the GP - who knows.

But what doesn't make sense to me is why school-based immunisations aren't comprehensive.

Year 7 and 8 students get immunisations at school - for schools that are participating. The kids there get their tetanus, diptheria and whooping cough booster, and the HPV vaccine. 

There's a national vaccinations register, so the public health nurses going into the schools to deliver vaccinations would know which kids haven't had their measles shots. 

So my dumb questions:

1. Why aren't vaccinations provided at all schools rather than just at some schools? It seems far more efficient to send one nurse out to vaccinate a year-cohort of 20-100 kids than to send 20-100 families each to the GP for a vaccination. 
2. Why aren't the public health nurses providing the MMR vaccine along with DPT for Year 7 kids for those kids who missed the shot when they should have had it? The shots are government funded anyway already, via the GP. But it's cheaper and more comprehensive for the government to provide them via the public health nurse who's already at the school than through GP offices. 

What am I missing? Is this a doctor-cartel thing where they really like getting the revenue stream from in-GP-office shots?

Thanks to @mikeythenurse for relevant discussion.