Well, here are my guesses - form followed function.
Until sometime in the 50s, most arms were straight. Then, when the importance of offset angle became better known, arm manufacturers designed "S" or "J" arms to achieve this angle. Also, remember at this time it became common to have a removeable headshell, something easier to implement with a S or J arm if offset was to be maintained. Next, in the mid-70s high compliance cartridge designs became more popular, thus requiring low mass arms. It was easy to see a straight arm would have lower mass, all other things being equal, so many lower mass straight arms with offset headshells were introduced. Then by the late 70s/early 80s, MC cartridges became more popular. Being lower in compliance (on average) they required higher mass arms. This time, realizing straight armtubes were easier and cheaper to build, manufacturers continued with straight arm designs but with higher mass, a practice continued to the present.
If you read fellow 'goner Raul, you may see that sometimes straight arms work best, sometimes S or J arm are a better match. Similarly, a fixed headshell should not automatically be assumed to be superior. In reviewing Raul's comments, you'll see that sometimes the surprising arm/cartridge match is the one which works the best.
Until sometime in the 50s, most arms were straight. Then, when the importance of offset angle became better known, arm manufacturers designed "S" or "J" arms to achieve this angle. Also, remember at this time it became common to have a removeable headshell, something easier to implement with a S or J arm if offset was to be maintained. Next, in the mid-70s high compliance cartridge designs became more popular, thus requiring low mass arms. It was easy to see a straight arm would have lower mass, all other things being equal, so many lower mass straight arms with offset headshells were introduced. Then by the late 70s/early 80s, MC cartridges became more popular. Being lower in compliance (on average) they required higher mass arms. This time, realizing straight armtubes were easier and cheaper to build, manufacturers continued with straight arm designs but with higher mass, a practice continued to the present.
If you read fellow 'goner Raul, you may see that sometimes straight arms work best, sometimes S or J arm are a better match. Similarly, a fixed headshell should not automatically be assumed to be superior. In reviewing Raul's comments, you'll see that sometimes the surprising arm/cartridge match is the one which works the best.