Here you are right Big-3 is main problem in ICC and cricket's better future specially Indian are doing dirty politics after introduction of IPL and having huge funds in their pockets.
But here concern is not IPL, and we are not talking why they are not allowing their players for other leagues and now allowing Pakistani cricketers in their league here is concern these all boards need to do some worth with ICC for having better structure and other facilities in countries where we can do some good for this game and youths can join this as professional cricketer which is increase its popularity, and we will be able to have some more good and quality teams in this frame.
I think the reason why the BCCI does not allow their players to play outside leagues is that first of all, they don't want to raise any potential competition and secondly, they are paying a lot of money to a lot of people in power and in that way they are doing what they think is best for them. Obviously, if they let the players play in other leagues, those leagues will also rise in popularity and maybe give IPL a good competition but by doing this they are eliminating any chance of that happening.
I agree with you that Big 3 is the main problem of ICC because they only need to evaluate a lot of good players in IPL and they are not paying proper attention to it.
Given the right price for cricket, youngsters can join it as professional cricketers which increases its popularity and we will be able to put some more good and quality teams in this frame. I hope the ICC will keep a close eye on this. This will increase the interest of every person in cricket.