If the buildings around you have a lifespan of 50-100 years and you aren’t replacing 1% or 2% of them every year, then you are falling behind. If population is growing due to births, increases in life expectancy, or an influx of immigrants/refugees then housing construction must account for that as well.
I'm currently renovating a 150 year old house that was previously majorly renovated 50 years ago and we're aiming for a useful lifespan just for the parquet/plumbing/electrics of at least 50 years, 100 years for the joists, insulation and plaster. The building will hopefully stand for hundreds of years.
Of course, pretty much only suburban areas have infrastructure/buildings built over that short an interval. Constructing 90% of a major city’s high rises in a decade would be a construction boom unlike anything the western world has seen in a lifetime.
Lifespan of a building isn't some kind of magical threshold thing where it is perfect for 100 years and then must be replaced in year 101.
A noticeable share of those buildings built for 50 years will need to be replaced around years 25-30. Almost all of those buildings will need work before 20 years is up. Some of them will outlast their design life by a large factor.
Not to mention that not every builder is selecting the same construction techniques and design life.