You only really NEED a FF camera if:

You are a pro and make your living with clients demanding the absolute best IQ (some will demand medium format - commercial ad or fashion photography!)
You are a wedding photographer and need to shoot the lowest possible noise level inside churches, for example, or other indoor shooting applications.
You are a landscape or portrait photographer (although APSC does a great job there too).
You shoot a lot of superwide angle subjects, real estate interiors for example.

FF will give you about 1.5-2 stops extra margin for acceptable noise levels. If you shoot at ISO 6400+ that will come in handy.

Everything else is a want...but we all experience GAS at some time or another. Keep in mind FF will demand great quality FF lenses, which are larger and heavier generally at the same focal ranges and f number. If you are a casual daylight shooter - like me - APSC is fine. I have the D7200 and it takes great photos with good noise control under ISO 10,000, especially in daylight, and sometimes up to ISO 18000. I use mostly FF lenses, anticipating my upgrade to a D850 or other FF body....I will still keep the 7200 for applications where a DX comes in handy, but the D850 also has a not too shabby DX mode 19.4 MP.

I'm reasonably certain many of us have worked our way up to a full frame camera after years of shooting with crop sensor cameras. The bodies are more expensive and the lenses are more expensive. In the beginning, you cannot really know if this is a hobby you will stick with. In the end however, those of us who stick with the hobby find ourselves with several camera bodies and various lenses to go with them. The choice is similar for many other endeavors. I play the saxophone and have about a dozen of them. But after 55 years of playing, I now only play the very best ones I own. It was a progression and a journey to arrive at this point.