Both because of a significant decrease in taxation but mostly because the plague, climate change and warfare killed half or so killed half of the people living in Europe at the time.

The same thing happened in the 1300s and 1400s as the number of people decreases significantly the quality of life for those who remained increased (more land per capita).

Additionally there were significant technological developments during the middle ages which resulted in higher crop yields (especially in northern Europe) (heavy plow, horse collars, wind mills, more water mills, 3 and later 4 field crop rotation, general improvements in metallurgy...

The 20th and 21st century havd been revolutionary from a medical point of view.

> When infant mortality is factored out (i.e. counting only the 67–75% who survived the first year), life expectancy is around 34–41 more years (i.e. expected to live to 35–42). When child mortality is factored out (i.e. counting only the 55-65% who survived to age 5), life expectancy is around 40–45 (i.e. age 45–50). The ~50% that reached age 10 could also expect to reach ~45-50; at 15 to ~48–54; at 40 to ~60; at 50 to ~64–68; at 60 to ~70–72; at 70 to ~76–77.

Early 19th century England

> For the 84% who survived the first year (i.e. excluding infant mortality), the average age was ~46–48. If they reached 20, then it was ~60; if 50, then ~70; if 70, then ~80. For a 15-year-old girl it was ~60–65. For the upper-class, LEB rose from ~45 to 50.

Less than half of the people born in the mid-19th century made it past their 50th birthday. In contrast, 97% of the people born in 21st century England and Wales can expect to live longer than 50 years.