I disagree with your opinion that people under 65k per month or people who care about 800k should not consider to live here. You would be surprised how many people can stay with less than that money. And no... they are not starving and also they don't live in a hut in the jungle.
Anyhow... you asked for reasons for change from retirement to DTV... I just told you that many people think about it because they want to get their money back. You are right...the 800k are not blocked for life, but 400k actually are. Lost money... until you can get it out somehow...
The DTV don't ask for any "safety" for living expenses... you show the money once and nobody will ask you ever again if you still have it or not, same with "income" as a freelancer. So... you can't compare this with retirement or marriage extension. Btw... since you are saying that one needs at least 65k per month to survive here... why are 40k enough when one is married to a citizen? Because the inlaws will feed him/her? I highly doubt that...
Not everyone on retirement extension is on pension already or have the 65k. Also not every embassy issues this letter for the pension anymore. Well... you may say 800k "is not that much", but for many people it's not "pocketmoney". And don't forget that 400k are permanent blocked... that's a big "fee" for the extension, no?