Because it's:
The most mobile TD and thus the most able to escape such a situation.
Currntly breaking balance and other tunes leave a hole in the usf lineup
The elefant has always been a hard counter to TDs, but even now the Jackson is the LEAST vulnerable due to its MANY traits that were used to keep it alive when it was squishy and only make it God tier now that it can literally brawl if it needs to.
Most of the problems with M36 come from its offensive performance at max range not from its HP.
Making die to 2 elephant/JT shots might lead to another elephant nerf...