There are loads of ways. I definitely hear you though OP, it is baffling.
Some people have inherited money.
Some people are holidaying at a property owned by family or staying with family.
People who can travel outside of school holidays have a huge advantage - having recently had to book flights over half term and being gobsmacked by the difference in price (literally 4x!!!!), I can say that if we were tied to school holidays we'd be holidaying exclusively in Scunthorpe.
Lots of people just prioritise different things - they might never eat out, never go out drinking, not buy expensive clothes and jewellery, not shop at Waitrose, not drive a nice car and so on. When I was a kid we went on really nice holidays but my parents were Scrooges about everything else.
For us - we have a airmiles credit card which allows us to get massively discounted long haul flights (for our last trip to South Africa, the flights were £500 return for two of us).
Also, we almost never book package holidays - you usually save more than 50% buy booking flights, car hire, accommodation yourself.
Finally - we nearly always go self-catering. DH have ulcerative colitis and too much rich restaurant food really knocks him for six so we have to really, but it comes with a massive costs saving.