It's like getting the truth about any sensitive question. Look at the incentives. Virtually anyone with access to the knowledge has incentive not to say it, at least not too loud.

You can find a few good scientists who will say it softly and politely. They all have to eat dinner with colleagues who have staked their careers on it. I don't have that problem. You can reason through it yourself from first principles. Solve the lindblad master equation with all the external noise parameters set to zero. It gives you the limit of SELF-decoherence. All the data ever gathered is consistent with lindblad. That's the wall between quantum and classical.

Here is an example of the soft, cautious, polite society version:

Mikhail Dyakonov** – Exponential control + decoherence caps QC forever.