I'll try to answer this. You can do what you are asking about on an in-line
engine, such as a 4 or 6 cylinder, but its orders of magnitude more
difficult on a "V" configuration. The reason is that the pistons and
connecting rods, with their studs, can't get far enough away from the crank
to be able to get all the caps off, hold all the rods away from the crank,
and lift the crank straight out. One set is going to bind or keep you from
doing it. And the worst part would be in getting it back together -
remember, the con rods are now holding new journal bearings.

I think the bottom line is that it is very difficult to position the crank
in such a way that you can avoid having at least one set of con rods get in
your way when you're trying to pull it.

Another reason is that if you're replacing bearings in the lower end for any
reason, it makes sense to pull the heads, replace the valve stem seals, and
put a set of rings in the holes... to do any less is simply inviting oil
consumption.

Those are my thoughts. Someone may have a better reason.
r/
Steve