Sometimes it can pay for itself to upgrade your car, yet there are a lot of trade offs, so you don't necessarily need to go from the current car that you have and into a new car, yet surely the market for used cars is going to vary in terms of what kind of quality car you might be able to get in terms of how much the price difference might be between new and used... but yeah, if you have a decently long timeline, such as 15 years or more, then it may well be worth it to start out with a new car and then you already know what you are starting with.. presuming that you sufficiently understand that some brand of cars might have better quality than other brands.
Conversely though, if you keep a car for 15 years, it is going to be 'old' and certainly not showroom fresh for most of it. So why pay a high premium for something you apparently don't value so much and rather get something still just as capable for a much lesser price at 1 or 2 years old.
With that said, cars are not being built to last any more for a while and it's become worse as time goes on. My car is from 2000 and while the engine is still in fantastic shape as I near 300,000 miles and wear-and-tear on the mechanical parts is only to be expected, the plastics on the interior (and in some other places) have aged horrible. It's only worse now with screens and apps that will be obsolete and irreplaceable within 10 years (you already see this happening with some early navigation systems). It's a shame as we seemed to hit an inflection point for longevity with engine quality and galvanized panels and then it all started getting worse again. Anyway, I digress...