whats the benefit for miner not to include some transactions???

[hamdi]

i saw that many of my transactions dont get included by many pools,
although i have a tx fee in my client...

so whats the benefit for them

[tiberiandusk]

They confirm transactions with higher tx fees. Or due to the randomness of who finds blocks your tx wasn't found by them.

[ForceField]

It would provide for a smaller file size and therefore be quicker to sync/download.