From the USGA website:
https://www.usga.org/RulesFAQ/rules_answer.asp?FAQidx=177&Rule=15
..."Q. May a player change golf balls during the play of a hole or a stipulated round? When the player is permitted to substitute another golf ball may he change to a ball of a different brand or type?
When changing balls, the player is permitted to substitute a ball of another brand or type unless the Committee has adopted the One Ball Condition of Competition (see Appendix I; Part C; Section 1c). This optional condition (usually referred to as ‘The One Ball Rule’) is generally adopted only in events that are limited to professional golfers or highly-skilled amateur golfers. Generally, this condition of competition is not adopted in club-level competitions...."
WGT's application here has absolutely nothing to do with the One Ball Condition, or Rule, as even the USGA acknowledges it is referred as. If it did equipment changes would be allowed in practice. Ball changes would be allowed in country club play if the club tournament committee so desires and it would be allowed in individual play where there is no competition.
The lack of substitution is more likely because programming choices into the game is too difficult or would make the game perform more erratically.