Because I don’t have enough time to play Global.
I like to have an historical style A&A.
Convoys rules are interesting for representing the economical effect on UK of U-Boats warfare ETO and on Japan of USA subs warfare PTO.
It is an interesting alternative to SBR.
Subs can be useful outside direct naval battle.
I put some HR and new units in 1942.2 (like antisub Escort Carrier, mechanized infantry, TacBombers) because it is a smaller scale than Global but still complex.
When I have only 2 or 3 hours with friends, we play 1941.
But it is not a game intended to have HR because even OOB rules from 1942 can ruined the balance.
We play it OOB rule only.