Many WGT players are not real golfers, or are casual golfers and aren't familiar with the Rules Of Golf. They wouldn't be expected to be familiar with the rules.
WGT uses a stroke average rather than a handicap and many aspects of WGT are tournament play necessitating the use of tournament rather than casual play rules.
So the other part of the ball situation here on WGT is found in Appendix I, Part C, 1., c of the USGA Rules of Golf.
The tournament committee is allowed to invoke a local rule/condition of the competition known as the One Ball Condition.
The One Ball Condition states that the player has to use the same make/model of ball during a stipulated round. A breach of the rule results in disqualification. WGT does not disqualify a player. Instead WGT provides a ball (the same ball to anyone who runs out of the make/model ball they started with) we can finish a stipulated round with.
WGT warns every player they are using their last ball of that make/model, and gives the player a chance to buy more of the same ball.
A player that chooses to ignore the warning and/or elects to not buy another sleeve of the make/model ball they need to be sure they can finish the stipulated round can't complain too much.