This is most likely due to the operator of a large pool using all the hashing power for merged mining but only paying out the Bitcoins. Any miners with a standard Bitcoin pool are expecting a certain payout in Bitcoin for their hashing power. Starting merged mining at the pool does absolutely nothing to change this (aside from possible a little server downtime) and so is a good opportunity for profit. If miners actually want the namecoins then there is a selection of pools which payout namecoins too.
This are the arguments everyone likes very much. Your opinion in other words:
"We can cheat everyone, who doesn't care about it!"
I hope every pool operator puts his cards on the table, to see who is not informing his miners about what is done with the miners shares on the miners payed electricity.
Well, i don't like to be scammed!
Don't put words in my mouth!
I would guess that most people mining at a standard Bitcoin mining pool are expecting a "fair share" of Bitcoins for their hashing power. By using the hashes to generate Namecoins I would argue that a pool operator is doing nothing to change this. I fail to see how any cheating or scamming is going on. No rules are being broken and no fraud is taking place. If a miner doesn't care about namecoins then this is a non issue. If a miner does care then they might consider using a pool which pays out the namecoins too; it's a free market.
If a miner actually has a moral problem with Namecoins (but not with Bitcoins) then there could be something to this but I honestly feel that most of the comments here are driven by personal greed and envy.
I dont understand why do even mine in btc-only pools, when u earn much more on merged mining pool..
If they wanna give away their nmc coins to pool operator whos back mining merged, thats fine, serve them right..
cheers
There are several reasons. Low variance, reputation, reliability, lower risk. Honestly though, with BTC income close to electricity cost for most and with merged mining offering a greater than 40% income bonus I would expect most people to try merged mining.