That is your belief. That is not how the bond market works. The price of credit reflects the supply of and demand for it. During the last 10+ years the Fed has created artificially high demand for long-term bonds through QE which has depressed yields. In addition, foreign governments (especially China) had to do something with all the excess dollars they had from running trade surpluses with the US. The safest place to put those surpluses was in US treasuries thus increasing demand (and depressing yields). Inflation "expectations" have had nothing to do with it. Any reversal of those trends (and we are seeing that) will increase long-term yields regardless of what inflation "expectations" are because supply will simultaneously increase while demand decreases.
People make what you might think are irrational economic decisions all the time. Why on earth would anyone purchase government securities with negative interest rates when there was no deflation? Maybe the picture is bigger than you think.
Well, Hmm. There is very little to debate here. You state that price is set by supply and demand, then you state drivers of demand, ignoring inflation expectations. Certainly price is set by supply and demand. But what determines supply and demand?
That inflation expectations are the key driver of longterm treasury rates is widely accepted in the financial community and among economists. But obviously there is more to that in play as you point out. But inflation expectations play into the thinking of sovereigns also as they purchase and sell bonds, an investment for which they require a positive return. Same with pension funds, corporate and individual investors. The idea that inflation expectations play absolutely no role, as you suggest, is hogwash.
Here is one article which explains this:
"In the absence of credit risk [I.e., with respect to US Treasuries] (the risk of default), the value of that stream of future cash payments is a function of your required return based on your inflation expectations. "
'In other words, the higher the current rate of inflation and the higher the (expected) future rates of inflation, the higher the yields will rise across the yield curve, as investors will demand a higher yield to compensate for inflation risk."
https://www.investopedia.com/articles/bonds/09/bond-market-interest-rates.asp
I guess it is possible the the massive market for US Treasuries reflects people making uneconomic decisions, but that seems quite unlikely.
And anyone thinking that would probably not be investing in such a market.