Camshaft theory

My advice is to forget a shelf grind and get a cam made for your particular combination.
It will require that you present flow numbers , real compression , end use and car weight , gear etc. etc. information.
But you will be much happier for it.
Will your car run on a " shelf " grind ?
Certainly.
And there might be an appropriate stocking cam for your deal , though the odds increase dramatically in this regard if you drive a Chevrolet.
Call Bullet and ask what they think.
http://bulletcams.com/
As for the " why " part of your question , the generic answer is that valve train stability wins when mapping a lobe profile for the masses.
You are not going to the dyno with four or five cams to see which wrings every last ounce of power from your deal and most likely have a set budget for valve springs and broken parts.
What they sell is a cam that will provide an increase in power with a minimum of side effects..........probably with a lobe that has been tried and true to another manufacturer's engines.

Edited to add..........it is no more expensive to have a spec cam ground. I made some concessions to streetability with my deal and could not be any happier with the cam we agreed on.
Your input matters to them and they work WITH you to get it right.