Because WGS would make PK level character look bad 
WGS simply mean they are too weak to compete for WSM, PK and Emperor titles, so they become best at ''sword skill'' only, its a pathetic title for top tiers.
WGS hides behind Emperor title:
If PK's underling can't even be WGS, PK would be disappointed:
Roger being Great Pirate also > being WGS:

WGS simply mean they are too weak to compete for WSM, PK and Emperor titles, so they become best at ''sword skill'' only, its a pathetic title for top tiers.
WGS hides behind Emperor title:

If PK's underling can't even be WGS, PK would be disappointed:

Roger being Great Pirate also > being WGS:




