After a couple years of lifting, you could potential exceed the limits of a standard bar. If you generically just lifting the same amounts with no training program to progressive overload (except not even sure why you would be doing this really) It's not like everyone will be powerlifting or strength training, but in the end of the day, whatever time under tension will make you somewhat stronger. It's the same reason you buy a 500-1000 lb rack, even if you're not lifting that much yet: you might. And what's the point of buying a 300 lb limit one, when you would probably exceed that some day? Sure most of us may never get to that "next maximum level" but a lot of us will be able to do 400-500 lb dead lifts 300-400 lb squats, etc. after a while. So there isn't much reason to purchase a standard set.
That being said, right now due to Covid stuff, even the standard stuff is selling for ridiculous amounts. But before that, it was usually far cheaper, or even free. So I suppose if things were free, you could use that.
I have the opposite thought most of the time: why do they even make standard stuff? I do actually have some (200 lbs) for a Bodyline cable system that I got for free. I guess the plus is that I don't have to move my Olympic plates over constantly to put it on the machine. (I do have some adapters if I needed to.) But for the most part, other than maybe back rows, where I sometimes put all the weight on it, 100-150 lbs is quite enough for most everything else.