Thing is the loan arrangement might be ok for the team offering the loan, no big benfit for the team taking the player on loan unlesd its a lower league team.
No incentive for wire in this case.
Bigger clubs can afford to take youngsters and players with potential and loan them sown the ladder or duel reg until they are ready to step up to first team level.

At the end of of the day a player will go to where the money is, depending on how good they are which is rightly so. It is the same for a player as what it is for you and I if you do not feel you are earning what you are worth you will move job for more money. Also remember a players career is very short 15 to 20 years at best so they need to earn as much money as possible during their short career. I think the majority of players are loyal to their club when they are under contract but will not or do not think about the community side of the club when their contract comes to an end
Broncos have a proven track record in development and bringing players through to a super league standard, these players will move on to the top super league clubs rather than stay at Broncos who do not have the long term prospect of staying in super league.

I'm not sure thats strictly true. Maybe its the lure of making it into a top team with the facilities and coaches they have at their disposal with the prospect of playing for GB. Naturally the money may come with that.

Not convinced playing for GB is main driver in many players minds.
Going to a bigger more successful club and being in with a chance of being part of a winning team, and maybe winning trophies more of a driver. Along with money.