Yeah I don't have every system of every gen but I do have quite a few (I had/have every system of last gen, at leastmy DS is gone but 3DS can play DS games anyway so it's w/e) and from here on out I intend to at least have good access to every systemall that's left for this gen is the PS4 which I intend to get as soon as I save up the money from disposable income.
Like other people said the biggest thing I can't afford is actually the time... if it was just as simple as buying the system's that'd be easy, but I have to have money to buy all the games for them and the time to actually play them, lol.
At the very least I try to prioritize Nintendo systems because they're the most fun for me, followed by PS systems, followed by Xbox systems. For people who can afford them all: good for them, they've either got a good job resulting in solid disposable income, or maybe they're spoiled or something (or I guess they could've won the lottery lol).
To people who can actually play them all: I don't think there are many people like that out there (most gamers I know tend to focus on just playing a few games instead of a large variety anyway) but good for you. It's not really my business and hey, if they can actually balance a social life, their physical health, a job, and whatever else with gaming, more power to them. But maybe they just don't care about any of that, and it's whatever. *shrug*