Why not use an arc'ed lathe?

I can answer part of this.

The actual mechanics of doing a radial cut on a lathe is not that profound. The problem is that the cutting sylus is good for about 10 hours on the outside. Each stylus seems to be different from every other stylus. So when its time to replace it, the replacement part is simple. The setting up the cutterhead to work the way it did before is not. That might take a bit of work getting it right.

Now setting up so that its tangental is hard enough and its something you that have to do and get right. Once its right at any point on the LP surface its right anywhere else too.  Setting up a radial cutter means that you would have to insure that the stylus is set up exactly right at two points on the LP. That would be about 10 times trickier!

Sounds just like setting up my linear tracker. :^)
Sounds just like setting up my pivot arm !

Yes. Now imagine that the difficulty of doing so is 10 times greater and has to be done very 10 hours of use!

'manufacturers like me'??

We've tried really hard to make our stuff plug and play; automated the bias, made it really easy to set up the amp (matched tubes not required) and such. I recognized 30 years ago that stuff has to be easy to use or it will wind up in a closet or worse.

'Manufacturers like me' have got nothing to do with it. If you want to give someone a hard time about it, talk to the lathe manufacturers? What's that?? you don't know any??

Sheesh.