What makes vaccinations "recommended"? (for Philippines)

Asking for medical advice on a forum, is probably not the ideal approach.

You really need to talk about where you plan to go and what you plan to do, with your family physician since they know your health history and a tropical disease specialist, as they know what you might encounter. Sadly travel vaccination clinics tend to have a broad understanding (similar to what you get from the CDC) rather than specific knowledge of each country and environment. And often err on the side of caution, over prescribing shots.

I think as a whole, Expats living in places like the Philippines get very few vaccinations, rather they adjust their lifestyles to mitigate the risks, such as using mosquito repellents when out in the forests to avoid being possibly bit by Dengue or JE or Malaria bearing mosquitoes.

But the fact that an Expat doesn't get inoculated, doesn't automatically mean you can avoid it too. You need to understand the risks and consequences first, then make your own decision.

I know you asked about US expats but I'm adding this for reference for others.

Here in the UK, generally when booking a holiday you can check the health service website which will tell you if vaccinations are required at all (just yes or no) and then you book an appointment with your GP/nurse.

What I have found (after booking a trip to Philippines) is that by the time I arrived at my appointment the nurse has already checked the most recent travel advice given by the government and checked the current status in terms of mosquito prone areas and any current outbreaks of whatever. Depending on where you go in the Philippines depends on whether you need additional vaccinations or anti-malarial drugs in addition to the usual mosquito protection.

For my trip the only additional vaccines I needed were Typhoid and Hepatitis A, as I already had up to date routine ones (and Revaxis - Diptheria, Tetanus and Polio from a previous trip to Brazil).