Not necessarily, a dropping admissions rate can be experienced even if the performance requirements remain the same and the number of unqualified applicants increases.
"for decades" that's somewhat debatable. Stanford has been renowned locally in California and along much of the west coast for decades. Its nation-wide renown and worldwide renown are more recent. Stanford started to see large growth in the matriculation rate and number of applicants in the mid to late 2000s and really kicking off in the 2010s. One year, I think in 2009, there was unexpectedly high matriculation to such an extent that freshman had to sleep in cots for a few weeks.
It's been a good University for a while, but I think it's reputation as an institution on par with Harvard or Princeton, or OxBridge is maybe 10-15 years old.
