My PIL are like this. They really aren't that interested in food in general, they never watch any TV cooking shows like Saturday kitchen or Bake Off and the only meal they cook from scratch is a roast Sunday lunch. Everything else is pre-prepared to put in the oven/air-fryer or out of a tin/packet/jar. They do not enjoy eating out and see it as a huge waste of money.
They are suspicious of anything unfamiliar and stick to what they know because of the fear of wasting money if they order (for example) a Pad Thai or a paella because they might not like it and not want to eat it. Far safer to stick to a burger and chips, or shepherd's pie.
Having said that, the beauty of All Inclusive or even B&B at a hotel overseas is that you can try things without spending anything extra. When we have stayed AI in the past the children have always been encouraged to try things - just a spoonful - see if they like it. If they don't, that's fine. DS developed a love for squid rings when he was about 3, daughter became obsessed with the salad bar.
PILs wouldn't know where to start with a buffet style AI offering, too much choice, labelling can be a bit suspect sometimes like a full description of the type of fish and sauce ingredients in Spanish, all it says in English is "fish". So again, default to the known and unchallenging.
We don't go on holiday with them.