Numbers do lie.
The increase isn't real. The same storms have been occurring but differences in detection and damage ratings have made it look like there are more. They're simply finding more that previously would have overlooked.
"On February 1, 2007, the Fujita scale was decommissioned, and the Enhanced Fujita Scale was introduced in the United States.
[6] The new scale more accurately matches wind speeds to the severity of damage caused by the tornado."
That alone changed quite a bit as far as numbers confirmed and their ratings.
While there are more documented and rated, were there in fact more in 2020 than there were in 1980? More than 1940?
There are also more people in more rural areas today than 40 or 80 years ago, so there are more structures to take damage and more radar installations to detect rotation.