You see them for the brief period between them being next to you to them passing you, as compared to cars, where they're in front of you for most of the time you're driving. There just aren't many cyclists in most of them, too, because most bike lanes are like islands, they connect nothing and exist for usually political purposes rather than to actually be a usable network of transport. In cities, this is not the case, mind you, there, bike lanes are usually interconnected enough that one could use them for many trips most of the way, but in the area I live in, where the bike lanes do exist, yeah, the cyclists will pass right by, so you don't even notice them unless you're at the intersection where they are. What might clear it up is that bike lanes where I live are mostly on straightaways and they give up when a major intersection comes up, the lane just ends, and it might start back up after, maybe.

To paint the picture, imagine it's rush hour, and there's cars backed up everywhere because that's just how it always is at rush hour. You're, let's say, 7 cars from the intersection, and a cyclist passes. You see them for a grand total of maybe 5 seconds before they're too far ahead of you to see, then they turn right at the intersection, and they're gone.