Ash, think you should have added Dogs and Dynasty to that list
Hiring guns can become a liability, we have seen examples players come in to the pits before the game, and leave at the end, spending little to no time with the team they are playing with, preferring to hang out and drink with their cool buddies on their trade stand. Not all US players are like this, but some have been and some of those may have a tendency to pick up penalties and cause controversy for the team they play for.
Those that get involved with the team can be a real asset, but to get them involved in the training programme per-event is not only an extra expense but can be fraught with difficulties due to schedules. Can you imagine if the PSP and the MS rounds were a week apart? Would the player be an asset then as he would probably not be able to fly out of the US until at least the Monday be fore the MS if the PSP event was the weekend before, OK, they could train on site on the Thursday for an hour, if the team can stretch to booking a training spot too, though this may or may not be the most productive scenario. And if the PSP were the weekend after, it is unlikely that a player would be excused to go play in Europe the weekend before, while the rest of his team were practising! That said, a few players can just drop in to a team and make a difference, but when you add entry fees, paint, kits, possibly air fares, travel, accommodation, meals and even remuneration in to the equation, that adds up to a ton of cash that the team could possibly better afford to pay on supporting their own players and/or developing upcoming talent.