Eliminating time limits on standardized tests is infeasible; it would require changes to processes on a state or national levels, and mindsets in education as a whole. It's also a complex enough issue that you'd have factions arguing for and against it six ways to Sunday. It's not going to happen.

In contrast, special-casing few disadvantaged students is a local decisions every school or university could make independently, and initially it was an easy sell - a tiny exception to help a fraction of people whom life treated particularly hard. Nobody intended for that to eventually apply to 1/3 of all students - but this is just the usual case of a dynamic system adjusting to compensate.

Eliminating time constraints is entirely reasonable. Leaving exams early is generally an option in most standardized testing systems - though usually with some minimum time you must remain present before leaving.

Taking what is currently scheduled as a three hour exam which many students already leave after 2, and for which some have accommodations allowing them 4 hours, and just setting aside up to five hours for it for everyone, likely makes the exam a fairer test of knowledge (as opposed to a test of exam skills and pressured time management) for everyone.

Once you’ve answered all the problems, or completed an essay, additional time isn’t going to make your answers any better. So you can just get up and leave when you’re done.

You say it is infeasible for standardized tests, but why? Is it that much harder to give 50 students and extra hour than to give 5 students an extra hour? Or just design the tests so that there is ample time to complete them without extra time.

But putting aside standardized tests, in the context of this discussion about Stanford, I think these accommodations are being used for ordinary tests given for classes, so Stanford (or any other school) has full control to do whatever they want.