Because great defenders don't always make great defences. It's partly about set up and partnerships. Some of greatest defenders have been cheap. Gallas, Hyypia, Vidic, Toure were all signed for barely anything but forged good partnerships and were solid rather than spectacular. Now granted they were signed a long time ago but most were for couple million and even in today's money only equates to what, £10m? VVD was only £10m from Celtic, azpilicueta was £7m, Kompany £8m?
Look at some of fees paid for Mustafi, Lovren, Sakho, Mangela, Otamendi over last few years. From 18m to £30m and none have been much good.
Forwards are more expensive because it's harder to score goals that's the main reason. Goals win games, you could have best defence in world but unless team score you're getting relegated.
I dont totally disagree with your point, I'm a defender myself so naturally on their side when it comes to arguing (think defending has been made harder in last 10-15 years because you aren't allowed to tackle anymore) but there's a reason forwards tend to earn the big bucks and get votes for POTY etc and it's because they tend to have the biggest influence on the team. A £50m striker will generally have much more influence on team than £50mmdefender. Because forward can have a moment of magic and win you a game from nothing but a defender could be superb all game, but still needs 3/4 others around him to do the same to keep a clean sheet. Defending is a team game much more than scoring.
