We're guessing at the reason, but here's what we think:

+ SWCG (salt water chlorine generators) have been less durable than the makers would like. This has shown up as they've reduced the warranty period on the units.

+ SWCG life is mostly a function of ON hours; lower the hours and the unit lasts longer.

+ At a constant chlorine level, high CYA reduces chlorine loss to sunlight. If you follow pool industry standard, you will have the same chlorine level at CYA = 30 as you do at CYA = 70. In the absence of algae, this will lead to less chlorine use, and less SWCG 'ON' hours.

+ So (we think) SWCG makers have latched on to this to make their units last longer.

+ But, maintaining constant chlorine levels over a varying CYA level is a HUGE mistake. This page explains more: http://pool9.net/cl-cya

+ We recommend the following:
1. Buy the largest SWCG that you can put on your pool, and then turn it down.
2. Never use your SWCG during start-up, or during an algae outbreak: manage those manually.
3. Never use your SWCG to shock; pour a couple of gallons of bleach in, instead.
4. Maintain chlorine levels in proportion to your CYA level; you'll need the K2006 kit in order to do so => http://pool9.net/test/

Those 3 steps above are the CORRECT way to reduce SWCG 'ON' time, and prolong your unit's life.