I mean just look at some lesser successful trucks that start kicking ass on international tours when a Grave Digger driver takes over. Plus, Grave Digger n Max-D use the best drivers around. Then who knows what everything else costs? I'd be guessing BKT provide the tyres at a discount, but they'd be mad to give away 100s of tires for free, so they probably supply certain teams free ones or a set amount and the rest are at discounted prices, but I'd suspect they mostly just provide a few free ones a year to the 5 or so most popular teams.
apart from Avenger who must have a decent amount in the bank to afford what he does to that truck. Afterall it is something like 10k per tire and the littler guys have less sponsors etc. Grave Digger and Max-D can afford to drive the trucks into the ground, where as other teams, especially the independents, try to take it more carefully so's not to damage the trucks too much and have to pay for repairs. However it could probably come down to how much more money some teams have. Especially if other trucks seem to not even be trying to win, driving slow, just cruising over obstacles and not putting their foot down. Sometimes it feels like Geave Digger is set up to win.