Because, in my view, the cross-code games acted to break down the barriers between the codes. Now, you can say that is a good thing, and don't be so paranoid, but of the Wigan team, look how many subusequently felt comfortable enough with the RU side of the ledger that they subsequently left RL for RU as a player or coach, or others (like Radlinksi) were targetted by RU. In comparison, how many Bath RU players tried RL?
Wigan:1. Radlinski, 2.
Jason Robinson, 3.
Tuigamala, 4.
Connolly, 5.
Offiah, 6.
Henry Paul, 7.
Shaun Edwards, 8. Cowie, 9. Hall, 10. O'Connor, 11.
Haughton, 12. Cassidy, 13.
Andy Farrell, 14. Smyth, 15. Murdock, 16.
Scott Quinnell, 17. Johnson.
Other Wigan players from that era also went to RU in coaching/admin, includng Joe Lydon and Billy McGinty.
Here's Farrell in 2003, speaking well before he went to RU (so his comments aren't RU-spin)...
Nonetheless, Farrell admits that his respect for rugby union has increased tenfold since the exhibition matches in which Wigan played then-mighty Bath in both codes. "I used to think it was boring. And there's that north-south thing, which is stupid, really. But I learnt a lot in that game against Bath about how technical it is - the rucking, the mauling, the line-outs, the scrummaging.
"It's a completely different game, in fact. You score tries, kick goals, play with an oval ball, and that's about it. Not half of those playing rugby union could play rugby league, and not three-quarters of those playing rugby league could play rugby union."
The Independent - Saturday, 20 September 2003
Sure, all of the above could have happened anyway in the post-RU turning pro era & Wigan had all the top RL players, but there is no reason RL should help it to happen - and the Bath-Wigan game smoothed the path for Wigan players to join RU (as Farrell has offered above).