It's a combination of laziness, greed, and short term thinking.

Laziness because ckpool code is out there, free. I've played with it myself. It's not hard, but it does take a small amount of effort. Any of the big pools could put forth this effort and get ckpool working for themselves, or design their own pool code that didn't SPV mine.

Greed because getting the 25 BTC block reward is more important to them than anything else, including processing transactions or ensuring that the block they are building on is valid.

Short term thinking because if they continue down this path and continue to drag the majority of miners with them, they will eventually cause another fork that will confuse people, especially outsiders, and reduce the overall trustworthiness (value) of Bitcoin.

I think there is something lost in translation because macbook-air doesn't seem to understand that he did threaten kano.is pool and he did lie. The point of the discussion on SPV mining is to get people to stop doing it, but it is being taken personally. As was mentioned elsewhere, there are plenty of ways to damage a SPV pool. Calling them out and trying to convince them to change isn't one of them. Instead of reacting with threats, macbook-air should be reacting with appreciation. The path to stop SPV mining couldn't be laid out any easier for them.