Because you are thinking about things in absolute terms vs. relative.

The 4% or 25x rule basically guarantees that A) a 4% withdrawal rate is X% successful over a 30 year period, and B) that 25X expenses sustains that 4%

If you target 25X current expenses in today's dollars, and your expenses are consistent with inflation, the 4% rule works.

If you target 25X current expenses, then suddenly expenses double outside of inflation, 25X of your expenses in the past is useless.

This is why the math in his "The Shockingly Simple Math behind Early Retirement" blog post works.

If $25k is $50k in the future, the accumulation formulas take that into account, if lifestyle creep is the reason behind that doubling of expenses, you are SOL.