Why the experimental method was most widespread in the 20th century.

This is due to the fact that it was the 20th century that became the century of scientific progress. Previously, scientists could not work at full strength. Religious leaders, who played a large role in society, strongly prohibited dissent. Many scientists were killed during the Inquisition. After the weakening of the influence of the clergy, development began in the field of anatomy, physics, astronomy and other sciences. This was already in the 19th century, but the experimental method was able to develop after some time, when a large knowledge and technology base had already been created for this.