Techmology: why do heavy, long coilover shock springs exist?

It occurred to me that I'm running a super long, 650 lbs spring which could be halved in (# of coils) length and reduced significantly for the same spring rate... unless I'm missing something (highly likely). This would save a huge amount of weight.

I did see that Enduro racers are running super short coils with spacers:

https://www.pinkbike.com/photo/12462828/

Unfortunately my crappy Marzocchi shock has threads way up on the shock, so it would require a pretty big spacer. The old Fox shocks that I once ran had much more threads on the shock body.