Can you just clarify a little more on what you have identified - "Most to many Americans through legal tax deductions/credits pay little to nothing for the first 50K dollars each year. In Thailand that number is reduced to around $4kand theoretically retirees would have to pay taxes on the amount above 4k that was never taxed if brought into Thailand."
I am unfamiliar with US Federal Taxation and am not sure if the "legal tax deductions/credits" that you identify if they are simply Tax allowances or they belong to some other method. For example in the UK there are available personal allowance on earnings £12,570, savings interest allowance (approx.) £6,000, Dividends allowance £500 (April 2024), capital Gains allowance £3,000 (April 2024). Hence it would be theoretically possible up to £22,070 is taxed at 0%. This means that all the £22,070 has been taxed and would be allowable for DTA (if all allowances are observed by Thailand).
Referring back to your post - If the first $50k is the equivalent to the UK £22,070 (taxed at 0%) isn't then in your example, the tax free amount available to bring into Thailand without being taxed, $50K rather than $4k.