Other architects managed to make buildings which didn't want to tip over.Those 900(ish) year old architects didnt quite have access to the same ground penetrating technology available today.
Lets face it, what architecturally designed building put up today is going to be still around in 850(ish) years.
And well designed buildings today typically don't have the goal of lasting
for so many centuries. Designers observe that many will become obsolete
due to factors like....
- Increasing land value in the future will mean tear down for a replacement
with more tenants per acre.
- Technology & tenant market changes mean they'll become obsolete.
There are actually buildings designed to last only a few decades, eg,
self storage buildings are planned for a business in an area where money
can be made until the land becomes more valuable, & has some higher
& better use. It's called "land warehousing" in the business.
Performance over a limited life is often good design.
A great example is a car. If it were designed last a million miles
for the average driver, it would have to be much more expensive.
But by the time it reached that mark, it should've been replaced
with something safer, more fuel efficient, & with more features.
And average drivers will want a different care before then anyway.