[Retroman]

A lot of the most emotionally triggering stories/most relevant and important revolved around Janet and Johnny and them being together...

They even had an episode devoted to how they met.
And proceeded to have a baby and have the majority of scene's shot round there house.

They were the last to survive the "horror" episode in the pub.

Everything just generally revolves around them.
The writer intentionally includes a little more emphasis on those two, so the viewers grow to love them more. They're a likable couple, and were pulled from the "Royale Family" especially.

So they really were a massive part of the show, if you look at things in more detail.