Well, they haven't introduced 5, let alone 10 year visas for those married to Thais and the much hailed 3 year or 10 year retirement visas don't seem to exist anywhere but on some embassy websites.
Of course they could introduce any number of new visa schemes, but sadly, none seem to be made with those in mind who have the most right to be in Thailand: those with Thai families.
Why are they only granted 1 year extensions of stay?
Surely, short of offering citizenship automatically after several years of marriage, they could introduce a 5 or 10 year multiple entry visa with a 1 year stay on each entry, only a 12 monthly reporting requirement (or none at all) and showing 800,000 or 1 million Baht in the bank?
Of course. Especially if you're Japanese. I've only ever seen citizens of countries like Sri Lanka be required to enter a country on a specific flight and in that case it was a flight from Bangkok to Phnom Penh.
No longer possible is incorrect. The DTV is a brand new visa. Either it hasn't been possible to open a bank account with this visa so far, or they don't know what it is and don't want to open an account for you. Try another bank/branch or seek out an agent.