Probably for a similar reason that we have a different method to the military for dealing with forced landings.
Tight turning circuits are all very well in high performance, high energy a/c flown by a skilled pilot who originally needed a curving approach due to not being able to see ahead because they were in something like a Spit or Hurricane, whereas in civvy street we are dealing with a totally different set of circumstances. For instance it is much easier to control traffic patterns with muti leg circuits, rather than ones with constant turns, it is easier to teach and fly, and far easier for people to able to judge wind drift than if they were constantly turning. It also allows people to have a longer approach and not rush them, which would invariably lead to a huge number of problems in training or with inexperienced pilots.
We don't have the problems of a lack of visibility or excess speed that military machines used to have.
This is the standard pattern as laid out, but if you wish to do something different, that's up to you, but you must fit in with all the other traffic that's around you.