Most of the others have already said what I'm about to say, but I'd like to ask if you really want to hear "Honey" by Bobby Goldsboro? Do you know anyone who wants to hear it? It hit #1 in 1968 and stayed there for roughly a month, but the people I know who were around when it was a hit don't like it. Most of them say they didn't like it when it was new either. Enough people, of course, liked it at the time to keep it at #1 for several weeks, but they don't like it today.
Something else to keep in mind is that having a #1 hit doesn't mean your song is popular or that you're going to endure as an act. Approximately 1 in 7 artists who hit #1 never have another hit, and they're not always flash in the pan acts either. Sammy Davis, Jr. hit #1 with "Candy Man" in 1972. He never hit the charts again, and you never heard much of "Candy Man" either after it worked its way back down.
The reasons hits become lost are probably about as many as there are lost hits. I can tell you my 18 year old niece thinks my music sucks. She might grudingly admit a handful of songs I like aren't bad, but she's never going to willingly listen to them. Each generation has its own sound, and most of those sounds don't even last the full generation. As some of the others mention, disco was extremely popular in the mid-to-late 70's, but only a handful of those records endure today. Keep in mind also that popular songs are relative. A bad song can be a hit when its competition is weak. When it's competing with decades worth of other songs, that it was a bad song becomes more obvious. Go back and look at the year "Honey" spent a handful of weeks at #1. Take a look at the competition it had in 1968. It outperformed songs that are considered better today, but it was, overall, a fairly weak year in music. The Beatles only had two songs that made the Top-100 for the year, and, of the songs I recognize on that list, I'd only willingly listen to about half of them.