Why is that? Unless your pensions are solely for govt/military service, the DTA explicitly states that Thailand has exclusive taxation rights on private pensions -- and the technical explanation further elaborates that this includes traditional IRAs.
Now, this "exclusivity" is trumped by the "saving clause" in the DTA, giving the US secondary taxation rights to those incomes designated as "exclusive" in the DTA. This "saving clause" is found in all DTAs, and is just a clever way to make sure you're paying someone somewhere taxes -- and there's not a "no non taxation" situation.
Thailand could write their tax code to exclude taxation on those incomes that the DTA says they have exclusive taxation rights on. Why they would want to throw away potential tax collections -- is beyond me. But they could do this, and it wouldn't violate the DTA, since it doesn't violate the spirit on no double taxation. It just means the US taxation on your IRA (required by the saving clause) is full blast, with no discount from non existent tax credits from non existent Thai taxation on your IRA.
So, when it comes to Traditional IRAs, it really makes no difference whether or not Thailand chooses to tax this remitted IRA -- unless the Thai taxation exceeds that of the US taxation on same IRA. Then, you'd be out of pocket for the higher Thai tax; but then there would be no US tax due, as it would be totally wiped out by the Thai tax credit. But probable situation would be the US has a higher tax bill: thus pay full tax bill to Thailand; and some tax to the US, albeit net of the credit for Thai taxes.
Thus, the saving clause makes any exclusion from Thai taxes of your IRA (or private pension) -- not a meaningful part of your financial planning. *
* Unless you hire Thomas Carden at AIT in Bangkok. He has an original thought that only the DTA with Thailand has IRAs excluded from the saving clause. Thus, only by being an expat tax resident in Thailand, and no where else, can you avoid US taxes on your IRA. Sound too good to be true? For sure -- but apparently the IRS doesn't have the resources to uncover this scheme, as many have used Carden to avoid taxes on their IRAs -- and have gotten away with it. Feeling lucky?