Oh, boy---this one again.
For those not familiar, many chart freaks are still ticked off, 40 years later, that Foreigner was "robbed" of a number one single by Olivia Newton-John's "Physical", which stayed at the top of Billboard's Hot 100 chart for ten weeks.
Singles sales peaked in 1974 and began a pretty rapid decline from there on. So a high singles chart ranking meant less every year that went by.
And, as I mentioned in this very thread, groups that tended to sell albums were likely to do less well on the singles chart, unless it was a non-album single or a single that preceded an album's release. Why buy a single of a song you already have on the album (I know there are people on this board who have reasons, but trust me, most people didn't)?
So while "Physical" peaked at number one on the singles chart, and "Waiting For A Girl Like You" peaked at number two, it's instructive to look at the album charts---where Livvy went double platinum, and Foreigner went six times platinum. Unless you're totally hung up on the whole "little record, big hole" thing, far more people bought a copy of "Waiting For A Girl Like You" than bought a copy of "Physical".