Because best efficiency available always cost more.
Here is table and you see only Titanium is very efficient under 10% load.
 

 
 
Same was when Gold was presented... most of people was Bronze, little Silver and Gold efficiency was expensive on beginning before become standard.
During years manufacturers will produce more and more Titanium and less Gold units and price will be better.
 
If some people use 1000 G2 or 1300 G2 or 1600 G2 example and don't need so much power, if 1KW is enough for them should sell their PSU without Eco Switch and invest only price difference for 1000 T2 with Eco Mode. Example someone have 1300W and his PC use max 750-850, than 1000 T2 is better choice and new 10 years warranty. Even Sleeve Cables are same and could be removed on other PSU.
 
 

I don't think you could notice a savings on your electricity bill by choosing Titanium over Platinum.  IT would take a very long time to recoup that $80 price difference.

The only time you'll really benefit from the energy savings is if your load warrants it. Every PSU has a varying efficiency curve and unless the load you are at most of the time is within the "sweet spot" no you won't really be saving much from Platinum to Titanium.  The energy savings are only worth over the course of a long period of time, not a short term.  However, more efficient components generally mean higher quality internals and therefore longer lasting by some margin but it's not always the case.