Because if he starts creating 5943-tx blocks, the penalty pool will be smaller, and so will the amount he collects per block. See scenario 1 here - if the big miner behaves as the small miners do, it's the same as if they're all small miners. He will get just 4.50 BTC per block, instead of 4.68. He can't have the cake and eat it too - not pay a penalty, but expect to reclaim it...
That's not the point. What prevents the
competition from pulling from the pool without contributing to it? I understand that it's in the interest of a massive node or cartel of nodes to mine large blocks, but only if they aren't undermined by their competitors, which can pull from the pool without paying any penalty themselves.
The nodes can't have their cake and eat it too... But they
can eat it. Ultimately, there would be no pool.
If there are several big miners, they should all create supersized blocks, and then every miner will enjoy the supersized blocks of the others.
Yes, they should, and this would be a cartel; where each is cooperating with each-other for greater profits, and it would break up in the same fashion as other cartels; Any member of the cartel profits more by not contributing to the penalty pool.