If this is easier or more cost effective than producing an actual Magnum length action like the CZ550, why aren't more manufacturers going to route?
Of course. More cost effective.
Would you prefer to keep 2 production lines (medium and magnum length actions) with machinery tools and workers, or only one line (medium action), and do a bit of modification, for one cartridge only: 375HH? (and by doing so, cover the world market including Africa and Asia for dangerous game)
Majority of modern factories abandoned 2 production lines, and kept to one production line for medium action.
This, in turn, resulted in the new era of short magnum cartridges. (and rifles with smaller magazine capacity)
Magnum length action production remained for smaller workshops, and elite classic market.
for example - CZ zbrojovka at its peak had:
Short action line: cz 527 (before ZKK 601)
Medium action line: cz 550 medium (Before ZKK 600)
Magnum action line: cz 550 magnum (before ZKK 602)
But this was not economically sustainable, as reckoned. So this all has phased out.
(When they phased out, new mauser 98, made by mauser Germany, jumped to 10000 EUR/US MRSP)
Similar choice like Winchester had another Mauser factory: Zastava.
They made rifles Zastava m70 (aka m98 clone) on medium action, and added 375 HH and 458 win mag to their catalogue. (and 458 win mag is medium length with 3.34 inch LOA).
Economically speaking medium action is best buy, you can fit inside medium actions cartridge's, and short action cartridges' without problem.
So: Majority of European factories today, are making rifles up to 300 win mag, and 9.3x62.
They dont bother with 375 HH, nor 458 wm.
The reasoning probably is: African hunting market is too small, and Asia is closed for DG. Who needs 375 or bigger any more?
There are few exemptions, of course.
One is steyr with their 376 Steyer caliber.
Or, Sako 85, produced in 6 action lenghts - now that is something.
Then there is American industry with various new (short magnums) you name them, 375 ruger, 416 rem mag, etc
But now, you have a picture. (at least from my perspective)