Proportional pools still exist because the regular miners who are getting robbed blind want them.
I guess in most cases they are not well informed. Proportional is very easy to understand while other PPLNS or even the geometric methods are not as easy to understand. I have to admit that before some of my miners demanded to choose another reward system I was fine with proportional too. Only after I wrapped my head around PPLNS and pool hopping I saw its benefits. However I needed to explain it to some of the pool members in order to convince them (http://blog.masterpool.eu/2011/11/pplns-facts-and-myths/). The other problem is that there is no benefit for pool operators to implement another reward system as long as the pool members are fine with its policy. It means more work, more testing, perhaps new errors. Thus pool operators will only move if miners put them under pressure by moving to non proportional pools. Fortunately I have some very insistent pool members which made me consider PPLNS
Perhaps we need something in between Menis technical abstracts and my very simplified blog post on the forum and on the Wiki. At the moment even if you heard about PPLNS or geometrical you are not able to find easy to understand information which are suitable for the occasional miner.
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