It's literal W3C policy:
https://www.w3.org/TR/html-design-principles/#priority-of-co...--- start quote ---
In case of conflict, consider users over authors over implementors over specifiers over theoretical purity. In other words costs or difficulties to the user should be given more weight than costs to authors; which in turn should be given more weight than costs to implementors; which should be given more weight than costs to authors of the spec itself, which should be given more weight than those proposing changes for theoretical reasons alone. Of course, it is preferred to make things better for multiple constituencies at once.
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However, the needs of browser implementers have long been the one and only priority.
Oh. It's also Google's own policy for deprecation: https://docs.google.com/document/d/1RC-pBBvsazYfCNNUSkPqAVpS...
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First and foremost we have a responsibility to users of Chromium-based browsers to ensure they can expect the web at large to continue to work correctly.
The primary signal we use is the fraction of page views impacted in Chrome, usually computed via Blink’s UseCounter UMA metrics. As a general rule of thumb, 0.1% of PageVisits (1 in 1000) is large, while 0.001% is considered small but non-trivial. Anything below about 0.00001% (1 in 10 million) is generally considered trivial. There are around 771 billion web pages viewed in Chrome every month (not counting other Chromium-based browsers). So seriously breaking even 0.0001% still results in someone being frustrated every 3 seconds, and so not to be taken lightly!
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