Many reasons DF. As Tobes said it's partly the people who go but it's also the gulf between us and the players now. Even the local players go and hide up in Formby behind electronic gates never to be seen other than at club functions or charity golf days. Add to that the transient nature of players, the team is totally different every year whereas when I started going you could name
next seasons starting XI nevermind next weeks

You felt like you knew the players, their strengths, weaknesses and characters too. The biggest difference for me though is the effect sitting at the game has on you....it simply isn't conducive to making lots of noise. If you had the same 45000 and half of them were standing there would be a hell of a lot more noise than with the same people all sitting down.
The original point (made by JB and Saint) is still valid though. You can see players who make the effort more when you are at the ground and yes it does give a certain affinity to those you know give their all game after game after game, Skrtel is without doubt in that mould of player. He's battled on surrounded by ****e for the past few years, Johnson/Lovren/Toure/Sakho flapping around next to him (and Ming flapping behind him) plus no protection from the midfield whatsoever. Remember back to us having an in form Johnson and Dagger though and Skrtel rarely put a foot wrong. He ain't a world beater but he IS the best we have right now (by quite a margin).
I have to add that in fairness to all our defenders they have a lot to deal with in a Rodgers team. Our defence is attacked far too often because of the terribly porous midfield and the full backs bombing forward. All of our centre backs (and the keeper) are given far too much to do game after game. It amplifies their weaknesses ten fold when compared to how they would play in a Rafa or Kenny style set up (or dare I say a Jose style set up).