You could say the same thing about cars, couldn't you? Or many other consumer products. And what about electronics?

I don't see folks throwing away bikes like toilet paper, as you put it. Most people I know have bikes, probably purchased more than ten years ago, and most from big box stores, but they are still in service or at least serviceable. It might have a flat, or the shifting is a bit off, but even bikes from big bikes stores can last a long time since the total accumulative riding they do is more like 100's of kms rather than 1000's. The biggest detriment to these bikes is neglect. Even if you leave a thousand dollar bike outside for long period of time year after year it would eventually become a piece of scrap.